Ok, so I just got back from having a looksee.....and you're right! The way they designed the diff doesn't allow the outer bearing race to spin! That seems really odd. The ONLY reason I can come up with is, it adds strength to the diff and the diff's output collars. The diff isn't resting entirely on the outputs when you put it in the housing. But it seems pretty clear that the outer bearing races are somehow spinning in the bearing seats in the housing. And that isn't a good thing. We're talking drag, motor strain/heat, friction, and possible melting of those seats, if you have a brushless model. I melted bearing seats in my Hyper TT, when I hadn't noticed one of the diff bearings had seized. Had to replace the whole housing.
However, the cars have been running just fine with that arrangement. So go figure. ?? Still, in trying to just turn the bearings by hand, it's impossible. I could turn the one on the opposite side, a little, but it just bugged me. So, I took an X-acto knife to it and whittled down the four tabs on top and the ring on the back to flat. The diff sits in the housing as normal. So........what the hey, Dromida? I only did one for now, to see what happens. But failing any unforeseen issues, this might just be the mod that needs doing on all. Try it yourself and see what happens. I'd think we'd get less rolling friction > lower motor temps.