See the reduction: there is a text-indent that makes text go over checkboxes. In Firefox this doesn't happen.
Created attachment 6980 [details] Reduction
Confirmed with stock 10.4.5 and nightly r13116. Additionally, the checkoxes aren't clickable for me.
See also bug 13292.
Still an issue in Safari 5.0.1, but seems fixed in ToT. I don't recall any changes that could fix this intentionally, so we should polish up and land this test.
Safari, Chrome, and Firefox all successfully show checkboxes without text overlapping.