Comment # 17 on bug 107390 from Harry Wentland

Looks like a faulty board that reports a port as connected when it shouldn't.
Windows driver has a policy to only report that as connected if it's DP, but
not for HDMI, which is likely why we've never spotted this before.

Do you have more information on your graphics card (manufacturer/model)?

Can you also print vbios_version?

As sudo:
cd /sys
cat $(find -name 'vbios_version')