Tuning change after instrument change

Sample score please

Confirmed

Workaround: explicitly change to bass clef

How did you add the instrument change? The pallet text is broken for transposing instruments, but adding the instrument change Text from the [Add] menu works ok. See #320828: Change Instrument Palette Text does not recognise current instrument leading to incorrect transpositions

I haven't tested changing to drums - are they treated as transposing perhaps?

I just added an instrument change text from the text palette. I'm not aware that this is different from the menu entry?
While drums are certainly not transposing instruments, they are treated different enough from 'normal' instruments, so yes, that other issue might well be related

But indeed the palette text is bogus, it works fine with the menu entry, even with a drum staff
So this is a duplicate

And using the menu is the better workaround

Not particularly related to the reported problem, but I also see the OP says "In a piano score: change the bass clef to some percussion instrument (e.g. Finger clap) for any number of measures and then change back to piano. " Adding an instrument change to either of the two piano staves changes the whole instrument, not just the half to which the change is applied. It is not possible to have upper stave = piano, lower stave = finger clap (snap?), unless the individual piano staves have been created separately as two different instruments each with piano sound.

Both the palette and the menu apply it to the selected staff. But indeed affect both.