I have not ever seen a device with this problem myself, so everything in this post is just a random guess. It probably could be that it is some kind of hardware failure related to partial screen updates (applications use partial screen updates when run in 'normal' mode). A workaround would be to modify X server not to use partial screen updates and always update full screen. This workaround will reduce performance, especially for video, but probably can make device usable for a bit longer.

I would recommend to try installing Mer on problematic devices and check if this problem can be seen in it. Because Mer currently uses a new version of X server which is missing lots of performance optimizations (it only uses automatic fullscreen updates), it may not suffer from this supposedly hardware fault.

But this is only a guess, I may be completely wrong.