Yup. Finally happened. Very odd, too, as I got a succession of very small and thin nicks all during one stropping session. Best I can deduce is that, although I was turning over on the spine in the correct way, I must have not killed all the forward motion at the instant the edge touched down. I was going faster than in the past and, of course, speed kills.

Here's what I'm doing in penance. Since it's the right edge that's nicked, I'm switching to holding the strop with my right and holding the razor with my left. Forces me to be slower since it's the non-dominant hand. Working so far.