Created attachment 301346 [details] Screen capture demoing the issue (GIF, ~4 MiB) In some websites, after hovering an element which changes the background, the original background is not correctly restored when the element is not hovered anymore. Check the attached GIF for a demo of how this looks when the issue is triggered by PhpReport (https://github.com/Igalia/phpreport). This happens both an AC and non-AC modes, but only in HiDPI: manually setting the window scale factor to 1x in GNOME Tweak Tool makes the glitches go away.
Created attachment 301347 [details] Even more background glitches in AC mode (without needing to hover-unhover) Moreover, when AC is enabled, there are additional background rendering glitches which show already as soon as the page loads, without needing to hover/unhover elements. It looks like those glitches could be related.
These are happening at least since WebKitGTK+ 2.14.4, and they also happen in the current Git “master” with MiniBrowser.
Carlos García suggested reverting r211967 (http://trac.webkit.org/changeset/211967). Doing that makes all the glitches go away (both in AC and non-AC modes). Adding Miguel Gómez (the author of r211967) in the loop as well, hoping that he can take a look at this.
We've decided to rollback r211967 and work a better solution for the scrolling problem. Due to that this is not reproducible anymore, so closing.