(Bug report courtesy of TK)
SymptomsOn DZ startup, all zones immediately go to yellow, but the HVAC never starts.
WorkaroundBring all calling (yellow) zones to "green" state by changing setpoints, then put setpoints back at the desired value. Even simpler, flip all calling zones off, then on again. The HVAC will start as expected.
BugfixSince the bug pops up rarely (there's no need to reboot DZ every now and then, it appears to be rock stable now) , symptoms are immediately obvious, and there is a very simple workaround, the priority is now being set to low.
However, note that a newcomer will be a probable victim of this but: an hour of fiddling with thermostat wires to connect the DZ actuator will easily put the house into a state that will make this bug fire.
But then again, whoever gets to that stage is probably stable enough to be unaffected by such a simple issue :)