I have looked for reports of this, but there are many ways it might be described, so I may have missed them.
In sound files produced from a score I have been working on there are sounds—notes and figures—which do not correspond to anything present in the score. Today I learnt enough about Play mode to examine the event display and identify the events corresponding to those sounds, and even succeeded in deleting them. They are things which were present in earlier versions of the score but have been deleted or moved, but which for some reason have persisted in the event display. Obviously, this should not happen.
If this issue has not been reported before, I shall try to find an earlier score version which exhibits the problem. If it’s a known bug, I shall hope for a fix!
The only occasion in which it is known that notes can appear in the piano roll in Play mode but not in the regular notation in Write mode is if the notes somehow have a negative duration, which should be almost impossible. If you can cut down an earlier version of the project to a small chunk that exhibits the problem, I’d definitely be keen to take a look.
No negative durations that I know of! But I can certainly cut down the file and send it to you. [Sent by email.]
Daniel has diagnosed the problem by email: The stray notes in the piano roll were on a divisi staff that was not currently shown because the divisi change that gave rise to it had been removed (and forgotten!). Re-adding the divisi change revealed the ‘ghost’ staff, and the remaining elements in it could be removed.
Thank you for “closing the loop” with this explanation.