Regression with opaque region for XWayland clients
It looks like !1049 (merged) introduced a regression, resizing X11 clients with server side decorations in Xwayland leaves black areas behind on the desktop (root) window.
Also, this makes black areas a lot more visible while resizing apps with NET_WM_SYNC.
This is very easily reproducible using "thinderbird" email client on Wayland/Xwayland.
For testing purpose, reverting commit 19814497 gets rid of the issues.
Edited by Olivier Fourdan