VDPAU (and xvideo) tearing starting from 358.xx

I noticed video tearing with 358.16 right when it came out for Fedora 23. Back then I decided it’s a rushed beta release and simply downgraded to F22’s Xorg 1.17 and older driver. Worked fine for months. Now that the new long-lived release (361.28) is out, I decided to give it another go.

Unfortunately, this new release also has the tearing problem. And this time, I tested upgrading and downgrading Xorg on the same Nvidia driver.

Vsync working fine:
355.11 - Xorg 1.17 [1]

Vsync not working, video tearing:
358.16 - Xorg 1.18 [2]
361.28 - Xorg 1.17 and 1.18

[1] That version doesn’t work with 1.18.
[2] This one I never bothered testing with 1.17, just downgraded and waited for new driver.

Programs tested: mplayer and mpv, both with -vo vdpau, opengl and xv; also vlc but only vdpau

Now, spending half of yesterday on building that stuff, upgrading-rebooting-downgrading-rebooting-etc., I noticed that for a second after login, I can play video without tearing.

Turned out, starting a web browser and navigating to any site with Flash content (even hidden) caused this. One visit and vsync is off for vdpau until Xorg restart! (Currently it’s flash-plugin-

So I turned off hardware acceleration in the Flash plugin, hit alt-ctrl-backspace, logged back in and surprisingly, can’t reproduce anymore! We’ll see for how long, but at least glxgears and Talos Principle benchmark didn’t break it.

Expected result would of course be for the driver to be immune to any silly program breaking video sync globally. And 355.11 was indeed immune, but then something broke.
nvidia-bug-report.log.gz (124 KB)