Odd phenomenon when you have different time signatures on Treble and Bass clefs.
I don't know if this is a one time glitch I experienced or what, but I had a treble clef in 12/8 and a bass clef in 4/4. After entering notes in the treble clef, I tried moving some notes from one measure to another measure that already had notes but was not a full measure. Musescore would not let me cut and paste the notes into the other measure. I got a weird message about filling out the tuplet before moving the notes even though it wasn't a triplet. I know what 3 8ths in a 12/8 measure are a triplet in a 4/4 measure.
Another weird phenomenon is when I had 12/8 in the treble and 4/4 in the bass, then I reverse that (12/8 in the bass and 4/4 in the treble), the tempo speeds up by a third. Weird.