Half-maximized windows jump on the secondary monitor move to the primary monitor after the last window in the primary monitor is closed. I've been able to reproduce this with every application that I've tried.

Here's a video showing this bug: http://www.youtube.com/watch?v=lR4jynXfm9U

Steps to reproduce:
1) Open some windows on the secondary monitor
2) Half-maximize some these windows on the secondary monitor
3) Open another window in the primary monitor
4) Close the window on the primary monitor

Expected result:
5) Nothing, no windows move

Actual result:
5) Half-maximized windows move to the primary monitor, remaining half-maximized; non half-maximized windows don't move

This is using GNOME 3.2 on Ubuntu 11.10.