I think there is a bug with octava notation when we use multistave notation. For instance, I cannot put octava on last three notes (G, A, B) in this bar :
Pb 8ctava.7z (303 KB)
Select the note.
Invoke the caret.
Use the up arrow to get the caret onto the right stave.
Invoke the Shift+C popover.
Type 8va Enter.
Use Space to extend the line - it won’t appear at all until you’ve hit Space once.
Great !!
It works !