Repeats issues (1.x)
There seems to be bug(s) that are showing up recently with repeat playback, so it would seem prudent to put them together into a bug report.
Firstly, there's http://musescore.org/en/node/11383 . While the first example file is not correctly written, playback does show jumping between two different lines when a repeat happens.
Second, there's http://musescore.org/en/node/11461 . While the ending repeat is not closed (matched), the first one is but it won't repeat until the second one is closed.
Third, there's http://musescore.org/en/node/11465 . This seems to be a perfectly valid MS file. When the first volta is adjusted to play more than once, then the repeat plays the second volta instead, and the playback cursor jumps between the first and last bars.
I don't know if these are related but they do show some very nasty playback bugs.