Playbck intermittent using repeat bars

To repeat a section of a song, I used repeat bars (2 bar lines with 2 dots) So when the song came to the end bar, it went back to the measure with the start bar to repeat that section. But on that repeat playback the sound was intermittent, only playing a few notes, then skipping several measures, then playing again, etc.

When I saved the song as a MIDI file and opened it in another program, there were 2 tracks of the Grand Piano instrument selected, the first being the original run through the song, and the second track being just the few intermittent notes heard on playback. So playback was working, but the notes had not actually been created for most of the repeat measures.

This means I can't use the repeat bar lines and will have to extend the song as all original measures. Has this problem been encountered before? I am using XP, SP3, MuseScore 0.9.6.

Thanks.............Don