Misplaced rit. and then crash

I'm trying to make a small and simple arrangement of Carol of the Bells. In the last bar, there is a small rit., but most instruments don't play.
First of it didn't make my accordion (Harmonika) part (that could be an issue by itself, but I can make that manually afterwards). When I open the part it doesn't use my name for the part, but has returned to "Accordian/harmonika". That is a bit strange. And next time I open MuseScore, it's gone again.

But the rit. from the last bar is placed at the beginning of the last line, and not at the last bar. If I force a line shift, it just put's it at the new beginning of the line.
If I try to drag the rit. the program chrashes!

The I discovered, that I could drag the endpoint and start point, so it looks right... (though it points to the bar before) but now the rit. is changed in the score to be both the last bars.
If I try to change the rit. starting point to the empty bar, it chrashes again.
Any ideas?