(know this isn't helpful, but) I just flashed up to 185 and I am unable to reproduce what you've described, Tony.

I am wondering if this is an additional symptom of the strange garbage-named filesystem entries you were/are seeing. If it was related, I'd expect some of your other subordinate playlists to exhibit the same strange behaviour as well.

If you download the top-level .m3u and view it in a text editor, is there anything odd in there?