Changing instrument merges voices… bug?

Dear all,
please check the attached file, it’s a Vivaldi concerto for violin and strings.
I needed to arrange it for guitar orchestra so I made a copy of this file to preserve the original and, in the copy, changed the instrument of each violin player to classical guitar standard tuning.
Doing so caused all multiple voices episodes in the solo violin player to get merged into upstem voice 1.

I’ve already corrected the edited file so I’m not sharing it, I hope you can reproduce this from the original.
Just change instruments from violin to classical guitar.

Thank you
Have a nice day
Concerto n 9 in D major.dorico (665.0 KB)

There are no multiple voices anywhere in the file you posted. Everything is in voice one.

I see what you mean, so the issue must have arisen before at some point.
There were several two-voice passages in the solo violin, I know because I have input them that way.
For sure I didn’t merge them intentionally, so if I manage to reproduce it again I’ll report back.
Thank you by now.