So I defined a shortcut for show and hide accidental.
I have a score that is in Eflat major, and Timpani (no Key sig) instrument for which I want to hide accidentals. In full score mode, I select all notes in the Timpani staff and type the shortcut for hide accidental. Works fine. I then switch to the part which is still showing accidentals. I select all and type the shortcut to hide them. Works fine, so it seems. Then I switch back to full score and the accidentals hidden before are unhidden.
How do I hide accidentals in both the full score and the part? timpani.zip (305 KB)
Does it help, after you’ve selected all the notes and hide the accidentals, if you then select Propagate Properties while everything is still selected? I also have a shortcut for this, BTW.
I suggest you hide them in one layout and then use Propagate Properties to propagate the changes to other layouts. (The command you have bound to a shortcut to set the property overrides the existing setting of the property in the other layout. I will need to think further about whether we should change this.)