It's very likely that your hardware uses a DiplayPort-to-HDMI adapter (LSPCon chip) internally. Such hardware is a known source of trouble. So yes, I think we can call the errors on HDMI output a driver issue.
When I connect the TV/AVR to the DisplayPort 1.2, LE11 plays all videos with 3D audio one after the other. There is no need to reboot after each video.
But there is always an offset between video and audio! The audio is not in sync with the video.
Avoiding to use the LSPCon chip is your best chance to make things work. I think there is a setting for an A/V offset somewhere.