Chrome Version       : 55.0.2883.54
OS Version: 8872.54.0

What steps will reproduce the problem?
1. http://codepen.io/Zoxon/pen/VjEyBa
2. Scroll

The image on the right should behave like background-attachment:scroll (since it has a transform), not background-attachment: fixed.

https://drafts.csswg.org/css-transforms/#transform-rendering says:

"Fixed backgrounds on the root element are affected by any transform specified for that element. For all other elements that are effected by a transform (i.e. have a transform applied to them, or to any of their ancestor elements), a value of fixed for the background-attachment property is treated as if it had a value of scroll. The computed value of background-attachment is not affected."

This has caused interop problems for Gecko which does behave per spec: https://bugzilla.mozilla.org/show_bug.cgi?id=1292499

I verified that Firefox 49 and Edge 14 behave per spec.
According to the Mozilla bug (https://bugzilla.mozilla.org/show_bug.cgi?id=735857) WebKit behaves the same as blink today.  Given the Firefox and Edge have this behavior in their stable versions, I think the compat impact is relatively low.  I think it's probably fine to consider this a bugfix (no intent necessary).

Some history on the spec side: https://www.w3.org/Bugs/Public/show_bug.cgi?id=17521