When using a dual-monitor setup, some focused half-maximized windows move to the primary monitor after clicking twice on a notification in the bottom. I've only been able to reproduce this using Firefox and Thunderbird, so this might be a problem with the way the handle their windows.

Steps to reproduce:
1) Open Firefox or Thunderbird
2) Half-maximize its window in the secondary monitor
3) Perform some action that shows a notification on the bottom right of the primary monitor (e.g. play something on Rhythmbox, mount an external drive)
4) Give focus to the application window opened in 1)
5) Go to the bottom notification bar, click on the notification to open it and then click on it again to close it

Expected result:
6) Nothing happens

Actual result:
6) Window moves to the primary monitor, half-maximized in the same position as it was

Here's a video I recorded of this bug: 

Note that the windows must be focused (4) and that the notification must be closed by clicking on it again (5). If a window is clicked for closing the notification (event (1)), then this bug does not happen.

Using GNOME 3.2 in Ubuntu 11.10