This is a bug to track the issue I mentioned on IRC where mustPaintBackgroundOrBorder in RenderObject.cpp needs to return true if you have a percentage background-size. This will need a manual test.
*** Bug 8466 has been marked as a duplicate of this bug. ***
Created attachment 7837 [details]
Here is a test case I made based on a test Mitz made for a similar problem.
Created attachment 7838 [details]
Image for test case
Created attachment 7839 [details]
Here is a patch that fixes the problem. I can't seem to reproduce thh bug with a fixed background size, so I think I only need to check for percent.
Created attachment 7840 [details]
Test case that works in Bugzilla
I just realized that the other test case won't find the background-image I specified, so here is a version of the test that links to an internet-based image so that the test works in Bugzilla. I will check in the other version, of course.
Comment on attachment 7839 [details]
I committed this fix.