EDIT: I figured out what I did wrong while writing this post. It turns out that the SD card I was using was previously used as a boot disk for a Raspberry Pi. While it was an 8 GB card, it had been formatted FAT16 with a 60 MB boot partition. The behavior I describe below was what happens when you run out of space on your SD card. I'm going to go ahead and post this for two reasons. One is to let people know what it looks like when you try to save to a full SD card. And Two, to make a software request that an error message be added to the camera software to let you know that your SD card is full instead of entering an endless save loop.
I got my camera today, and everything was in great shape. Only issue was the backfocus screw not being tight (ended up turning the C-CS adapter when I installed the lens for the first time).
My first shoot was the obligatory water droplet, and everything went fine. Marked in and out, and saved. mp4 file works fine.
My 2nd and 3rd shoots were the obligatory lighter strike and a small firecracker exploding. On both of these, I marked in, marked out, and hit save. The save buffer went through the marked frames, but then it started over from 1 and went through all 8700+ frames...repeatedly. It got stuck in an endless loop both times, and I had to hard reset it both times. The files created during this process are corrupted and won't play.
For comparison, my successful water droplet video is 14 seconds long and ~35 MB. The failed videos are 4 MB and 2 kB. I think the size of those files is a function of number of frames it was at when I hard reset the camera (the second time it happened, I knew to look for it, so I reset the camera right after it restarted saving from frame 1).