Crash after bar line repeat forgotten

Hello again,
Just crashed computer about ten times trying to figure out what I did wrong.
See attached MuseScore file.
Went to play back a Mozart piece I was inputting, went to play (after sorting the playback thru I/O), and kept crashing.
If you look at the attached you will see that what I did was forgot to put in the repeat bar line at the beginning of the 15th measure so that the second section repeats from the 15th measure. As soon as I put the repeat in it all works ok again.
Maybe a "beep" or something to remind us that we forgot something instead of crashing?
Dave
(windows vista)