Comment 84 for bug 254468

It indeed IS the case for nvidia, I myself seen it on both nvidia and intel.

Perhaps in more recent ubuntu nvidia's version works better, didnt test enough.
On nvidia it was less likely to happen, perhaps because usually more video ram (to be used, avoid re-using of not-cleared pixmaps)

For me, on Ubuntu 9.04 amd64 on nvidia - I did not seen this problem for some time now, will test for next week.