"The issue is that after the hotplug interrupt is sent by the hardware, the monitor is not yet ready to respond to the DDC probes and generates a NAK instead - this leads us to conclude that there is nothing on the other end of the connector"
so it looks like a genuine upstream bug in the Intel graphics kernel driver.
Chris Wilson said this on IRC:
"The issue is that after the hotplug interrupt is sent by the hardware, the monitor is not yet ready to respond to the DDC probes and generates a NAK instead - this leads us to conclude that there is nothing on the other end of the connector"
so it looks like a genuine upstream bug in the Intel graphics kernel driver.