Blank lines ignored at top of text elements
This is definitely a regression and a serious one in that existing scores may depend on the current behavior to accomplish certain layout effects. It was discovered in a score that uses blank lines in an instrument name to force it it to center a staff name between two instruments, but it's easy to reproduce this in a lot of other less esoteric cases.
1) default empty score
2) edit title to add a blank line before the title
3) exit edit mode
Result: the title jumps up to the top of the frame. The blank line is still there, it's just being ignored to the purpose of aligning the top. So, basically, the box is too tight. I might have thought I could trick MuseScore into not doing this by adding a space to that blank line, but no such luck.
So this affects the positioning of any element with top or center alignment. It also affects how frames are drawn. So another way to reproduce:
4) click the rest in measure 1
5) ctrl+M to add a rehearsal mark
6) type a blank line then a letter
7) exit edit mode
Result: the blank line disappears, and the rehearsal mark shows the frame around the letter only. Again, the blank line is still there, it is just outside the frame.
Blank lines below the last line of regular text are not affected, they work just fine.