Created attachment 33243 [details]
I've seen a couple of pages lately where the page background does not fully paint on page load. One of them is Oliver's fluid dynamics page. I'll attach a screenshot.
This site appears to suffer from something similar:
if you click the links on the left a few times.
Created attachment 49935 [details]
Glitch on omnidesignltd.co.uk
An image of the glitch on omnidesignltd.co.uk on webkit r53397
Comments in bug 34913 say it's a dupe.
*** This bug has been marked as a duplicate of bug 34913 ***