Seemingly random instrumentation in MusicXML

I have a composition for 2 violins and 'cello. When I saved in .xml format and played it the first violin was played as a piano (the instrument of the last score I had played before opening and saving the trio), and the 2nd violin as plucked strings. The 'cello was still a 'cello. I deleted the .xml version and saved it again (after first playing it so MuseScore would be thinking "strings"). The 1st violin and 'cello lines are pretty much ok (multiple instruments rather than solo) but the 2nd violin is still plucked. :-(

Slurs and ties are messed up, too - tying only 2 adjacent notes together rather than extending over multiple notes. Worse, a measure consisting of a quarter rest followed by 3 slurred quarter notes was changed to a quarter note, a quarter rest, and 2 quarter notes. The slur is written between the first two notes, extending across the rest. It's played as originally written, though (except that it's being plucked).