There seems to be odd behavior in Chrome 15+ when using this particular combination of CSS properties, namely an outer element with visibility hidden and fixed positioning a
Yep, there is a bug, definitely: I managed to reproduce it in my version of Chrome too.
In case you'll want to fix it, you could add the “webkit's hasLayout” fix, -webkit-transform: translateZ(0); to wrapper or inner element, this makes Chrome to render the block properly.
Here is a fixed fiddle: http://jsfiddle.net/kizu/bHzWN/6/show/