When the upper left corner is either too far to the left or too far up, a window will be moved off screen in compiz 0.7.8.
-Move firefox such that the left edge of the window is off screen.
-At a cli, type firefox http://www.freedosktop.org/
-The firefox window appears to disappear, or move mostly offscreen, or in general move for no apparent reason to move it when it already has a place..
This doesn't happen if Place is disabled. Readily reproducible with Fedora10 and Ubuntu 8.10 compiz packages.
Fixed in commit