Empty beats/measures can't be selected or refilled in UI
You can have empty beats (or I don't know how to name it better, in german you would probably say "leere zählzeiten") which have _neither_ notes _nor_ rests. This seems to happen in the first voice only by accident / error, in the second voice you can easily produce this if you
1) enter three notes in the second voice: N, Ctrl+I, Ctrl+2, C, C, C
2) delete the note in the middle: CursorLeft, Delete
3) and delete the rest as well: Delete
This is a nice to have feature and correct behaviour I think, because you often only need a few notes in a voice and you don't want to have the rests around it.
But: If you want to fill the gap again, you are in trouble, because if you
4) select the first note by clicking with the mouse
5) enter some notes: D, D, D
the first note is overwritten as expected, but then the cursor jumps right to the next note after the gap and overwrites that to, so if you want to have your hidden beat back, your only choice is to select the note before it, increase it's duration (to a half note in our example) and than decrease it again to it's original value.
If the "gap" is in the beginning of your score though, your only chance is by deleting the whole bar.
I don't know whether to call this bug report or feature request, but I would like this to behave in a more convenient way.
Low priority therefore.