Two staves counted as one

I have two staves counted as one and I need to disconnect them so that they play in sequence rather than simultaneously.

I split a complicated score into two parts - the first part had an error which I was able to correct by deleting the corrupt measures and pasting in the correct measure from a different location in the same file. The second part was converted correctly and I was able to paste that into the resulting file with both parts working.

One set of staves came in as a piano and voice part. I changed the voice part to piano but the two staves still playback at the same time rather than sequentially.

I also noted that the treble clef of the copied measures appear in the bass clef at the back when the affected treble clef has Show courtesy enabled.

What am I missing?

Thanks in advance.

Update -
Describing this helped me come up with a solution. Copy the connected stave and delete the old range. Delete the extra treble clef on the the bass clef line. Insert three new measures and swap with the clipboard. Repeat process with the prior stave so that in effect I removed and replaced the two connected staves. They are now reading as separate.