Master Palette Closes Musescore Automatically

I'd like to write a passage in 7/8, but 7/8 doesn't exist in my palette. So everytime I try to open the master palette to make the new time signature (either by manually opening it or pressing Shift+T), it automatically crashes musescore and closes everything. Occasionally when it does this, it deletes some of my music too. I was wondering if anyone else had this problem or knows how to get around it.

I included the file below, it's mm. 15 I'd like to switch to 7/8.