[CSS2.1] Fixed z-index interop issue

Hello everyone,

We have discovered another interop issue involving a fixed position box with a child that is relative and has a z-index. Here is an example: http://jsfiddle.net/bh6tdww8/show/

In that example Gecko/IE show a yellow square while Blink/Webkit show a blue square. I believe this is a bug in Blink/Webkit because if you switch the blocks to a position of absolute instead of fixed, Gecko/Blink/IE/Webkit all show a yellow square. http://jsfiddle.net/bh6tdww8/1/show/

I looked at the spec regarding stacking contexts[1] and positioning[2];  and I didn't see anywhere that states that when fixed positioning is applied that it should behave in a different manner than absolute in relation to these areas.

Thoughts?

Thank you,
Greg

[1] http://dev.w3.org/csswg/css2/visuren.html#layers
[2] http://dev.w3.org/csswg/css2/visuren.html#positioning-scheme