Creating joined score with less instruments/staves in subsequent scores vs. the first yields corrupt score
To reproduce, create and save two new scores with different numbers of parts. Go to File -> Album…, click New, and click Add Score twice to add the two scores to the album. Click Join Scores and save to any location. When you open the joined score, MuseScore 2 will find durations of 0/1 and open with the warning "File corrupted." What's happening is that additional staves are created to maintain the same instruments throughout, but the newly created measures are not filled with rests. Instead, they're entirely empty—the worst kind of corruption short of an unopenable score.