Created attachment 263437 [details]
Attached testcase shows wrong behavior.
Created attachment 263438 [details]
This is happening because when we generate the keyframe style, we don't repeat the background-size into the FillLayers for each of the two background images. Not sure yet where to fix that.
Created attachment 263999 [details]
Comment on attachment 263999 [details]
Clearing flags on attachment: 263999
Committed r191589: <http://trac.webkit.org/changeset/191589>
All reviewed patches have been landed. Closing bug.