Key Signature Change for Single Staff Doesn't work for a particular staff...but it works for others

Hello All,

Score file attached.

I was trying to change the key signature for a single staff midway through the score, but it would not let me.

I followed the directions found at https://musescore.org/en/handbook/4/key-signatures:

Adding a local key signature for a single staff

If you wish to add a key signature to only one staff, leaving others unchanged, apply one of the following methods:

Select the measure from which you want the new key signature to apply, then press and hold Ctrl (Mac: Cmd) and click on a key signature in the (Key signatures) palette.

Press and hold Ctrl (Mac: Cmd), then drag a key signature from a palette on to a measure.

I found that this worked for literally ALL the other staves in my score, but NOT the one I wanted.

I'm trying to make the change at m. 17 for the staff labeled "Perc. 1".

If you open the file, you'll noticed that I figured out that I can just make the key signature for that staff invisible, which is really all I need. But I would like to know if this is a bug or if I'm missing something in case I need to actually use this feature in the future.

I tried changing the key signature for other individual staves. That all worked fine.
I tried changing the key signature for ALL the staves at once. It changed them all except for the one I needed.
I tried changing the clef back to a treble clef and not a neutral clef. That made no difference.

Thanks!

~Justin

P.S. FWIW, this score was originally created with the last version of MuseScore 3, but has since been altered and saved many times in 4.