In the posted video I'm demonstrating what happens regularly with 29.97DF. Sometimes it's after nudging ahead or back many times in rapid succession but sometimes it just starts out broken. At this point the nudge dialog gets confused and starts to frame advance always, with both hotkeys. The advance one seems to push on at 5 or 6 frames at once whereas the reverse one seems to advance (forwards in the project) at a rate of 1 or 2 frames at once.
The session in the video is 48khz with a 29.97DF timecode ruler. I've tried to replicate with other timecode settings but I can't get them to act up.