[Android Q&A, Help & Troubleshooting] xdmeh:
Thanks! Don't think luck will be enough to fix this though... I'm still not even really sure if what I'm doing makes any sense at all.

Ok, I so ran this:

Log.d("Widdebug", "BEGIN");
AppWidgetManager manager = AppWidgetManager.getInstance(this);
List<AppWidgetProviderInfo> infoList = manager.getInstalledProviders();
for (AppWidgetProviderInfo info : infoList) {
Log.d("Widdebug", "Name: " + info.toString());
Log.d("Widdebug", "Provider Name: " + info.provider);
Log.d("Widdebug", "Configure Name: " + info.configure);
}
Log.d("Widdebug", manager.toString());
Log.d("Widdebug", "END");

[/code]

On the broken phone it just gives me (nothing T_T):

01-01 02:50:08.710 21500-21500/com.example.test.qwerwidg D/Widdebug﹕ BEGIN
01-01 02:50:08.714 21500-21500/com.example.test.qwerwidg D/Widdebug﹕ android.appwidget.AppWidgetManager@41d5fca0
01-01 02:50:08.714 21500-21500/com.example.test.qwerwidg D/Widdebug﹕ END

edit: And the same again with verbose, there is that weird nonprintable thing (scoll right) again that I noticed earlier already while using launcher3 . Still don't know what that should tell me or if it's just a red herring:

01-01 03:03:16.470 29893-29893/com.example.test.qwerwidg D/Widdebug﹕ BEGIN
01-01 03:03:16.473 718-984/? V/AppWidgetServiceImpl﹕ getInstalledProviders hostName = com.example.test.qwerwidg������������������������������������������������������������������������������������������������������
01-01 03:03:16.473 718-984/? V/AppWidgetServiceImpl﹕ permission of the launcher: -1 enableFiltering = true
01-01 03:03:16.475 29893-29893/com.example.test.qwerwidg D/Widdebug﹕ android.appwidget.AppWidgetManager@41d60c60
01-01 03:03:16.475 29893-29893/com.example.test.qwerwidg D/Widdebug﹕ END

On a borrowed, working tablet, it gave me this output (as comparison - looks fine I guess):

08-27 14:47:15.180 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ BEGIN
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.android.settings/com.android.settings.widget.SettingsAppWidgetProvider})
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.android.settings/com.android.settings.widget.SettingsAppWidgetProvider}
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: null
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.google.android.googlequicksearchbox/com.google.android.googlequicksearchbox.SearchWidgetProvider})
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.google.android.googlequicksearchbox/com.google.android.googlequicksearchbox.SearchWidgetProvider}
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: null
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.google.android.googlequicksearchbox/com.google.android.apps.sidekick.widget.PredictiveCardsWidgetProvider})
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.google.android.googlequicksearchbox/com.google.android.apps.sidekick.widget.PredictiveCardsWidgetProvider}
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: null
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.android.browser/com.android.browser.widget.BookmarkThumbnailWidgetProvider})
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.android.browser/com.android.browser.widget.BookmarkThumbnailWidgetProvider}
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: ComponentInfo{com.android.browser/com.android.browser.widget.BookmarkWidgetConfigure}
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.android.deskclock/com.android.alarmclock.AnalogAppWidgetProvider})
08-27 14:47:15.280 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.android.deskclock/com.android.alarmclock.AnalogAppWidgetProvider}
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: null
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.android.deskclock/com.android.alarmclock.DigitalAppWidgetProvider})
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.android.deskclock/com.android.alarmclock.DigitalAppWidgetProvider}
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: null
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.android.email/com.android.email.provider.WidgetProvider})
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.android.email/com.android.email.provider.WidgetProvider}
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: ComponentInfo{com.android.email/com.android.email2.ui.MailboxSelectionActivityEmail}
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.google.android.gallery3d/com.android.gallery3d.gadget.PhotoAppWidgetProvider})
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.google.android.gallery3d/com.android.gallery3d.gadget.PhotoAppWidgetProvider}
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: ComponentInfo{com.google.android.gallery3d/com.android.gallery3d.gadget.WidgetConfigure}
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.google.android.gm/com.google.android.gm.widget.GmailWidgetProvider})
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.google.android.gm/com.google.android.gm.widget.GmailWidgetProvider}
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: ComponentInfo{com.google.android.gm/com.google.android.gm.ui.MailboxSelectionActivityGmail}
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.google.android.apps.books/com.google.android.apps.books.appwidget.BooksAppWidgetProvider})
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.google.android.apps.books/com.google.android.apps.books.appwidget.BooksAppWidgetProvider}
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: null
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.google.android.music/com.android.music.MediaAppWidgetProvider})
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.google.android.music/com.android.music.MediaAppWidgetProvider}
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: null
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.google.android.music/com.google.android.music.homewidgets.IFLWidgetProvider})
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.google.android.music/com.google.android.music.homewidgets.IFLWidgetProvider}
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: null
08-27 14:47:15.290 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.google.android.talk/com.google.android.apps.hangouts.widget.BabelWidgetProvider})
08-27 14:47:15.300 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.google.android.talk/com.google.android.apps.hangouts.widget.BabelWidgetProvider}
08-27 14:47:15.300 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: ComponentInfo{com.google.android.talk/com.google.android.apps.hangouts.phone.WidgetAccountPickerActivity}
08-27 14:47:15.300 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.google.android.calendar/com.android.calendar.widget.CalendarAppWidgetProvider})
08-27 14:47:15.300 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.google.android.calendar/com.android.calendar.widget.CalendarAppWidgetProvider}
08-27 14:47:15.300 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: null
08-27 14:47:15.300 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.android.chrome/com.google.android.apps.chrome.appwidget.bookmarks.BookmarkThumbnailWidgetProvider})
08-27 14:47:15.300 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.android.chrome/com.google.android.apps.chrome.appwidget.bookmarks.BookmarkThumbnailWidgetProvider}
08-27 14:47:15.300 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: null
08-27 14:47:15.300 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Name: AppWidgetProviderInfo(provider=ComponentInfo{com.google.android.apps.docs/com.google.android.apps.docs.widget.CakemixAppWidgetProvider})
08-27 14:47:15.300 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Provider Name: ComponentInfo{com.google.android.apps.docs/com.google.android.apps.docs.widget.CakemixAppWidgetProvider}
08-27 14:47:15.300 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ Configure Name: ComponentInfo{com.google.android.apps.docs/com.google.android.apps.docs.widget.WidgetConfigureActivity}
(... and many more...)
08-27 14:47:15.320 28319-28319/com.example.test.qwerwidg D/Widdebug﹕ END

I guess that confirms without doubt that there is a problem (independent of launchers).... uhm... but:

How do I squeeze any useful information from AppWidgetManager on where this problem is? Or something?