Exporting parts reverts stave changes made

I downloaded a file created by another member all written on the bass cleff for Trombone. I changed the instruments to treble cleff ones and made some octave changes. If I export to pdf the complete score it all looks OK. If I export all parts then they are all changed back to bass cleff (see attached).
I can get round this by hiding all parts but 1 then exporting the 'whole' score and doing this for each part but that's not ideal!
I am using the app image version on Linux