Sager NP9377-S keyboard lockup + shutdowns

So I have a really weird shutdown problem happening with my Sager NP9377-S (specs in signature). I just got it back from the LPC-Digital RMA service people with a GPU fan replaced; confirmed just now that the problem is still happening.

So what goes on is that while I'm playing games (or at least, it hasn't happened outside of them) the laptop's keyboard will suddenly lock up for about 5 seconds (ie, if I was pressing W at the time, the operating system still thinks the W key is pressed even if I let go of it) and then the laptop spontaneously loses power. Reboots without issue.

While the issue occurs only in games, it seems to happen independent of power draw (I've had it occur in graphically demanding games like Space Engineers but also in games as simplistic as Minecraft, Terraria, or Super Motherload).

I have extensively tested with various benchmarking applications (unigine, 3dmark, ycruncher, etc) and can confirm IT IS NOT AN OVERHEATING PROBLEM in either GPU or the CPU, despite what it sounds like.

Judging by the fact that the support techs asked me to mail in my power supply brick and did not replace it I'm guessing that's not the issue.

So now I'm at a loss for what's wrong. I'll have to open up another RMA, obviously, but...I don't know what to say. The keyboard thing is obviously centric to the issue but I have absolutely no idea how. Any advice/suggestions on what to say/opinions would be very welcome.