Tuplet brackets show incorrectly when only a single note
1) Create a tuplet from an existing note/rest
2) Change the length of the first note/rest to be the full length of the tuplet (e.g. a dotted 1/4 note in a 3:2 tuplet)
3) Observe that that tuplet bracket is drawn incorrectly (the right hook is to the left of the number, and the left hook to the right)
While this particular case isn't so useful, when there are tremolos involved, it's definitely useful for a note to display as the full length of the tuplet. In the case of a between-notes tremolo, selecting the first note and trying to enter a new pitch cause the same problem (and unexpectedly removes the second note - though this seems to be bug in general with replacing pitches for between-note tremolos).
At a minimum I'd expect the hooks to be swapped around to drawn on the correct side of the number. And perhaps better if the tuplet is just automatically removed in such a case (unless it's a single-note tremolo, in which case perhaps just hide the brackets). Further the number should be horizontally centred over the stem in the direction its pointing (it looks like MuseScore always tries to centre it over what would be an upwards pointing stem, even if it's downward). There's also a good case for removing the dot if it's a triplet.
Ref: Elaine Gould "Behind Bars", p 215, p 219.
Incidentally for tuplets such as 5:4 I don't really know how you'd do it at all, as there's no way of having a note that exactly divisible by 5 units (you can have 7, but not 11, 13 etc.). So maybe that's the real problem here!