GPU flattening causes video to freeze until playback restarted
Steps to reproduce:
- Download video file.
- Run Gallery app (or VLC with full acceleration enabled)
- Start playing the video
- Click on pause
- Wait ~1s to trigger Flattening
- Continue playback
I'm not 100% sure bug is caused by flattening, but it very likely to be so.
Also need to test on rpi4, where write-back flattening is present.