Sound Devices Recorders are a bit notorious for getting hot. A mixer once said to me you could "fry an egg" on his. While you do need to watch that it doesn't get too hot and turn it off when you can, it seems to be just a quirk you have to deal with as a sidenote to its other useful features.
I have 14 744Ts. They all get hot. Depending on how you use them, they can all get VERY hot. You know that cheat sheet that you can put on top of them (plastic sleeve)? They make those things start shriveling up from the heat.
So yes, it is perfectly normal for this to happen. As @Sean said, they are notorious for doing this, especially when in a bag.
I have a production mixer friend who inadvertently fried his SD 302 about 3x (and repaired by SD) before discovering that if both his mixer AND recorder's phantom power were enabled, it fried the gear. So it could be a phantom power issue of some sort too. But I hear SD is very good with customer service so you should be in good hands.