When an input element with 100% width is placed inside an unpadded div with to overflow: hidden, the focus ring around the element is obscured by the edges of the div. It is possible that this is by design, to fit with the CSS rule to hide overflow on the div. But it seems logical that, for accessibility reasons, the focus ring should not be obscured by any page elements. Otherwise, web pages could obscure the focus ring altogether. Noticed at http://www.avclub.com/content/node/57616 . Tested on nightly build r19107, Thu Jan 25 6:27:48 GMT 2007.
Created attachment 12676 [details] reduction for focus ring obfuscation
Confirmed as a regression.
<rdar://problem/5166151>
This is working as intended.
Closing due to Dave's comments in comment #4.