Literally empty, unchangeable, unerasable bar

While working with my score (see attachment) (and probably with triplets, as far as I remember), I somehow ended up with an empty bar in the trombone, the bar before the last bar. I don't remember exactly how this came, but this is the result. I can not erase or alter the bar from within musescore.

I was experiencing a possibly related bug before: When overwriting a triplet containing a crotchet and a quaver with a non-triplet crotchet using the repeat function with keyboard shortcut r, the quaver remained in the bar and was not overwritten.