Webkit button: background color overflows round corners

I'm trying to make a rounded button using -webkit-border-radius

This gives me this button (in Safari):

You ca开发者_StackOverflown see that the background color overflows in the rounding. I tried changing border size and radius, but it doesn't help. Is this a rendering bug with Safari or something?

It's addressed here on http://tumble.sneak.co.nz/post/928998513/fixing-the-background-bleed?d1dc0f00 Mike Harding's blog:

-webkit-background-clip: padding-box;

Looks like this is a rendering bug with WebKit. Adam Betts on Twitter:

We're at Safari 5 and border-radius artifacts is still here. Why isn't this fixed already? http://lensco.be/test/border-radius-artifacts/