Two staves to one while dropping the bracket?

[Alex Klein]

Hi,
a month ago I had a little problem which I still haven't found a
solution for. I was engraving a piece of music where the first violin is
split into upper and lower voice, which was notated by using two staves
and a group bracket. At one time in the piece, the split is lost and all
first violins play in unison. I was able to drop the second stave, but
no matter what I did, there was always a group bracket around the single
stave left.
What is the correct way to engrave this?
Cheers

Alex