I can confirm the bug, I already noticed it some time ago but since it didn't really bother me I never took the time to report it nor even to check whether it was already reported. It's not specific to a particular desktop environment or display manager. You also don't need to logout from the Xorg session to trigger it, just switch from Xorg to a tty and then back to Xorg and you'll get the same result. Personally I noticed the difference in the output of glxinfo -B or glxgears. For me this happens with the Intel driver (i915kms), since you mentioned drm-kmod but not AMD I guess it's also the case for you? I didn't pay attention whether this also happens when using the nvidia driver, I'll try in a few days at work where I have such a setup. Unfortunately I don't have hardware with AMD graphics to compare.
