> Really? It's surprising that the output name would change even with DC
> disabled.

Sorry, my fault. I tampered with the xorg.conf to match it the new naming with
DC enabled.

BTW, another interesting point:

I use dual-boot with Win10. I have never got the third monitor working with
Win10, because the Windows driver does not detect the monitor neither.
Initially, it does not appear in the monitor list, if I press the button
"Identify" the third monitor pops up as an "Unknown, Not PnP, VGA monitor", but
is greyed out. In other words the new Linux DC code behaves more similar to the
Windows driver (which of course is not a real advantage).