As you, I'm not expecting it to be fixed with this change.
Can you add a test.pass("...") here, to see if we get any open event?
It might be that, when you try to access window.tabs.activeTab.id during open event, 
one of the attributes throws. I can easily see activeTab to fail...
So may be additional checks like this could help:
test.assert(window.tabs.length)
test.assert(window.tabs.activeTab)
test.assert(window.tabs.activeTab.id)