hmmm, I just tried it and Thermal Turbojet/Thermal Nozzle aren't exploding when on reactors but when putting on a Thermal Receiver they blow up nearly instantly.
Am I doing something wrong or is it still releated to this bug/imbalance?
I have just a H2 Tank, Mk1 Inline Thermal Receiver and the Thermal Rocket Nozzle with a few Radiators. But it explodes faster than the radiators can heat up.