Comment 4 for bug 762335

What Timo said sounds right. The problem persists even if a window is a few pixels away from the edge. I must give it a significant buffer (10px?) for it to only show on the appropriate desktop.

This effect also "wraps". I often have a terminal on the left edge of the left desktop (in a 2x2 arrangement), and a maximized browser on the right desktop. When I try to use the scrollbar of the browser (on the far right), I end up resizing the terminal by dragging its left edge into the desktop.