I use my Diamond 9000HD on the DVB-S2 RTV channels on AMC3 daily and never have any problems. It runs barely warm to the touch and I think is one of the least buggy of any of the DVB satellite receivers I own. Mine also is running the original factory software. The only thing I have encountered (and I forget now where it is) is that some TP somewhere makes it reboot if scanned.
I also agree that I seldom have any such issues with my Diamond. I WISH that my Diamond had the factory firmware, but I bought it used, and it has the infamous 1.31P pirate firmware on it, even though the seller (some fellow in Ottawa) assured me that it had the original factory firmware on it.
But I use my Diamond to move my 90CM Fortec, and it also controls the switch that selects between that and my fixed Primestar dish, and the Ku LNB from my BUD.
I've never had the above mentioned problems with DVB-S2 transponders, either 8PSK or QPSK, although I too have run across one or two transponders that seemed to play havoc with the receiver. However when that happened, I rebooted, went back to the transponder, and wasn't able to repeat the problem, so I'm not sure what was going on.
My 9000 also generally runs quite cool, but one day this summer, the thing did seem to go beserk and it got very hot, and froze up, however again, after power cycling the thing, it came back to life, and has been running cool again for months.
Anyway, the OP'ers symptoms are strange. If it were mine, I think I would put my CM meter on the thing, and see if the LNB/motor, etc might be drawing too much current or something. I think normally, there should only be about ~90-100 mA current, unless the receiver is driving a motor, and then it might go up to a couple hundred mA. But if something's wrong with the LNB/motor, or switches, or wiring, maybe the power supply on the receiver is being over-worked.
Anyway, the Diamond IS really a nice receiver (if only I didn't have the pirate firmware). The only weird thing is that you need to use the channel editor to program DVB-S2 transponders. And that's one thing the OP'er might try, ie assuming that he has saved a copy of the channel data, last time the editor was used, it wouldn't hurt to send that to the receiver again, just in case the data in there got corrupted while in storage.