[BUG #7267] - Problem in qx.ui.mobile.form.List when changeBubble event ...

Bug fix for http://bugzilla.qooxdoo.org/show_bug.cgi?id=7267

qx.ui.mobile.list.List does not react correctly on a change of a property of a
model contained on the array.
On a string property, change is only applied if old string length is same than
new string length

Playground test : http://goo.gl/FYW2a 

Comment on commit introducing the bug :
https://github.com/qooxdoo/qooxdoo/commit/a5e7fa14ce9c5491ac905fdb4009fbc4d88fa10b#commitcomment-2703010