Losing staves

I run Musescore 1.3 on an iMac OS 10.8.4

I am inputting music for a Bach piece which includes a soprano staff and two piano staves. About 1/4 of the way into the piece, I started losing staves. If I work on the soprano line, my piano staves disappear. If I delete all empty measures and then append new measures, I get all three staves -- but once I start inputting on one of the staves, I lose one or both of the other two. I tried reloading and restarting. Not sure what to do next. I couldn't find this problem on the board.

Attached is the file -- at this point I've started inputting the piano bass clef, and you will see that the soprano staff is gone. If I add new measures and start working on the soprano staff, the subsequent piano staves disappear.

Anyone have any clue?

Thanks,

Emily