I just found out what provokes Onefang's crash with loading his files given here:
viewtopic.php?p=156085#p156085
I could reproduce it by creating two projects:
Project 1 with a single midi track, a single midi part, saved while the piano roll was open.
Project 2 empty but for project notes being nonempty, set to show at loading.
Close MusE, delete ../projects file, open MusE, open Project 1, open Project 2: Crash.