Thought I’d post this here because it may come up sometime and somebody may find it that way.
Description:
When pressing ‘play’, then ‘stop’ and then ‘play’ again, the cursor would stick at the first position and the play button would flicker. The song would be stuck at the first line, playing it over and over. The only way to get out of this was to click ‘stop’ as fast as I could.
Fix:
In my brilliance I had set an internal midi port as a midi device in preferences and the same port as a midi clock master, sending, among other things, start and stop commands. The idea was to route timing and stuff between applications not connected by rewire. Somehow I must have set one (like the midi clock master), then forgotten about it and set the other (the port as a midi device) later. I refuse to believe I was stupid enough to do both at the same time (although my wife would disagree).
The effect obviously was that every time I pressed stop and play and stop again there would be a feedback loop of stop/play transport commands, blocking the song at line one.
But hey, in my defense: I caught it just before I posted a bug report here and before I started harassing the developer of the plugin I just happened to be using when it happened. But only just. 
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