Is this really a bug? I always thought this was an intended feature. I use (or exploit, I guess) it all the time because its difficult to keep the high level (HEC-247) reactors always filled with fuel because of the low quantities of isotopes obtained from breeding.

Ah, you know what, you're right - I must have just got confused with the 1.11.2 version, where heat doesn't affect the power output anymore :P