For years I've suffered from a particularly irritating bug with X: when moving from one screen to another with the mouse, the cursor gets wedged between the two screens, bouncing back and forth. The X server uses 100% CPU time, and the only way I can get out of it is to terminate the session.

I've done a lot of head-scratching about the problem, wondering what it might be. On the face of it it's a bug somewhere in the X server, but it's interesting to note that it happens when the system is heavily loaded, or when some unusual activity occurs on the USB bus, such as attaching a new device. But I can't think of a way to chase it. Even debugging the X server doesn't seem to offer much hope.

On 30 September 2012 I got a message from Andrew Hout pointing me to a fix. I installed the new version of the nVidia driver, and sure enough, the problem didn't happen again.

Well, not for six weeks or so. And then it happened again, with marginally different behaviour. And it carried on like that for a while, every so often.

Then on 7 January 2013 I built a new kernel, and since then the problem occurs relatively frequently, noticeably in connection with attaching devices to the USB bus. So I'm back to considering that option again.