Misplaced GTK Xwayland decorations

A very clear example of this is firefox:

  • Window is resized from the inside and not from its borders:

Screenshot_20200509_012713

  • Context menus and the page scroller do not appear under the mouse pointer:

Screenshot_20200509_012810

I can also reproduce with other applications such as pamac-manager (which requires GDK_BACKEND=x11 to work in X11 mode). The problem doesn't occur with native Wayland clients. It cannot be reproduced if the application is maximized.

Software versions:

linux 5.6.10
mesa 20.0.6
Plasma 5.18.5
KF5 5.69.0
Qt 5.14.2
kscreenlocker v5.17.90.r20.gf2c89ed
libkscreen r1525.fe0bad4
wrapland 0.518.0.beta.0.r21.ge623d28
libwayland 1.18.0
wayland-egl 18.1.0
xwayland 1.20.8
libxkbcommon 0.10.0
libinput 1.15.5
libdrm 2.4.101
libxcb 1.14
libx11 1.6.9
Edited by magiblot