MS4: How to add underscores to multi-note words

Hello. I'm transcribing choir music. I first do the Soprano, then I copy it over the Alto and change the notes (it's quicker than entering all the notes again from scratch), then I repeat the process with the Tenor and Bass.

So, I have a word that stretches over two notes in the Soprano, Alto and Tenor instruments, but which has only one note in the Bass instrument. When I edited the Soprano instrument, I used the underscore after the word to create the underscore after the note that is usual for when a word stretches over more than one note.

But when I added the Bass instrument, where there is only one note at that point, all the underscores at that point for the Soprano, Alto and Tenor instruments disappeared!! It's as if the lyrics of the instruments are somehow "linked" to each other and each instrument does what the other instruments do.

Indeed, if I add an underscore to the Soprano instrument, an underscore automatically appears at the same position of the Alto and Tenor instruments' lyrics (how can I disable this feature, by the way), but as soon as I try to stop editing, the underscore disappears... and I suspect is has to do with the fact that the Bass instrument can't have an underscore at that place.

But I want the underscore at the Soprano, Alto and Tenor lyrics. In our choir, the Sopranos don't look at the Bass lyrics while singing the Soprano part. Any ideas? See image attached.

Samuel