I get the recursion error described in #122 with 2.0.0b4. The fix in that thread seems to help.
This has recently surfaced as mopidy/mopidy-spotify#49 too.
Currently I can't reproduce this. I could blindly disable the playlist_update_in_progress event in the hope of it making sure this never happens again. That doesn't feel like a very good solution, and we'll be left without that event forever.
Thus, I opt to close this issue until it resurfaces again, in the hope of ending up with a better solution then.
playlist: Register callbacks iff there is an event listener
Hopefully, this will remove the precondition for bug #122, #153, and #165.