Associating an instrument/two staves, with another/one staff, in an album?

From this pull request: https://github.com/musescore/MuseScore/pull/1588/files
I thought now that it might be joined in an album an instrument with two staves (e.g. piano) and another instrument with one staff (e.g. guitar)

So I made an album from these two files:
- test in G piano.mscz
- test in D guitar.mscz

Unexpected result in the reopening of the new file: test album piano-guitar.mscz

Ok for piano. But for guitar, we received also two staves! In the top (initial) staff, the clef has changed ( treble clef instead treble clef 8vb).
We can replace it, so it is not real handicap

Much more boring, as we said, the guitar receives a second staff - with a bass clef (and the keysig in G) -, that it is impossible to remove: you cannot select it.

And the change of instrument (in Staff Properties: Piano -> Guitar) does not change anything.
Have I misunderstood something? Thanks.