It CAN rotate when firing, particularly depending on the angle of the cut end, which I'm pretty sure is why my slide has failed to lock back after the final round in the magazine a couple of times.

I also DID request and receive a replacement recoil assembly, where the cut angle wasn't as sharp, but it may be only coincidence that I haven't had the lock-back problem since then. It wasn't a major improvement, and I still have to be careful with the rotation position when reassembling.

Now, the most recently built Shield I was able to examine a couple months ago had a MUCH better recoil spring assembly, a flatter cut end on the spring, the main spring had a better finish and a closer fit to the rod, so it didn't bow out anywhere near as much to the side. I suspect these newer Shields won't be having the same recoil spring related problems.