Comment 12 for bug 61105

As I see it, it can either be caused by two things:

1. It's a problem with the applications. Many implement mouse movement in games by for each game update resetting the mouse cursor to center of the screen - this is suitable for tracking relative mouse movement (for instance in an FPS game, you can roll your mouse for ever and ever (given a long enough chord :)), and the player will continue to rotate - if the cursor wasn't reset to the middle of the screen, the player would stop rotating when the cursor hit the edge of the screen).
This should work fine, but it's easy to make a bug in a game where the input loop is updated also when the application isn't focussed. Especially when using a high-level library like SDL.

2. It's a problem with SDL. Maybe some SDL functions unexpectedly resets the mouse cursor in some special cases.

It's weird that the bug isn't consistant on all system, though.