I have the latest release version of compiz and I noticed that when a window, eg. a normal terminal window was snapped to the bottom toolbar, but still hung over the screen on the left or the right, problems arose. The window would never completely lock to the bottom, because there was always one side that was not completely flush with the bottom toolbar. After I let go of the window, the window starts to shake around and eventually pops off the bottom toolbar and lands about 50 pixels above it.