Description of problem:
Selecting a  collapsed thread in the thunderbird thread pane and then trying to delete the complete thread by the delete popup menu entry (or by pressing the delete button) sometimes fails: some mails of the thread remain unerased. The worst case: I have to select and delete again (and again) for easing the whole thread (or after expanding the thread, selecting and deleting _all_ messages)

Version-Release number of selected component (if applicable):

thunderbird-9.0-4.fc16.x86_64

How reproducible:
mostly.

Steps to Reproduce:
1.select a collapsed thread in the thread pane
2.Press the delete button
3.
  
Actual results:
sometimes (not always) the thread is deleted

Expected results:
every time the thread is deleted

Additional info:
1. I'm sure that this thunderbird feature was OK until some previous thunderbird version (don't know, which version)
2. A thunderbird upstream problem?