Issue changing the clef of the first bar
Adding a clef to the first bar in a system in certain ways does not change the clef used by the system, instead displaying both clefs, with one of them intersecting either the key signature or the time signature.
To reproduce, select whatever is the first element in the first bar on the system and add a clef from the Palettes menu. Alternatively, drag the clef onto the element. MuseScore now displays the glitched second clef.
I'm running MuseScore 4.0.1, revision 9b70a8c on Windows 10.