I'm not sure if the bug has been fixed already or not, since it stopped happening to me around the same time the last post was made here, but for those who may be interested...
I've done a fair bit of troubleshooting with this bug and have found that, as someone above I believe mentioned, the problem is in the client side heat gauge. The heat gauge displays the incorrect heat value, so while in reality you may only have 50% heat gauge, your client shows it as having been over 100% without damage for a while.
Likewise with shutting down and taking damage at less than 100%, the heat gauge on your client shows say only 50%, whereas in reality you're running around with 100%+ heat.
The bug appears to remain consistent from match to match using the same mech... as in all my AWS-8R games presented the same, all my games with my dual ATM9 SHC presented the same, etc. Other than that I couldn't figure out any consistency to it... the bug appeared whether I was using newtech or not, whether I was clan or IS, whether I was in a light, medium, heavy, or assault, didn't seem to follow engine size or number of heatsinks, or heat rating in mechlab.
I posted specific tests and results in another thread at
https://mwomercs.com...heating-glitch/ if anyone's interested.