Grand Staff: Voice 1 always in Bass Cleff
Whenever you create a Grand Staff, Voice 1 (Rests) fill both the Treble and Bass Cleffs. It's easy enough to add Alto (Voice 2) to the Treble Cleff. But, in Bass Cleff, even after adding Tenor (Voice 3) and Bass (Voice 4), there is still Voice 1. Eleminating Voice 1 is almost impossible (if indeed not possible).
The smart thing to do is to have Voice 3 (or 4) automatically fill the Bass Cleff (with rests) upon creation of the Grand Staff.
Then, click on the Bass Cleff and provide the option to fill it with the other Voices (3 or 4) (Rests). That would be intuitive to the users needs.