Paul_o_b - 6:54 pm on Jun 7, 2011 (gmt 0)
I see a difference in Safari 5.05 PC and the same on my mac but it's only a few minor stray pixels and not as bad as the OPs original screenshots - but background-clip does fix it on both. (I do have a screenshot online but didn't post it in respect of your link policy.)
Unfortunately background-clip has the opposite effect in opera 11 and the whole background floods in the corner and is unusable so care must be taken to avoid opera seeing background-clip when using border-radius.
I expect that older Safari are even worse but I don't have an older version to check with anymore unfortunately. There well may be variations between systems, browsers and perhaps the actual size of the radius.
It would be interesting to know all the details in the OP's screensshot (system,browser version and styles used etc).