In my example, I have hidden note above the staff, of which I have also hidden the the ledger lines in the full score. In the part, the note is hidden, but the ledger lines aren’t - the corresponding box is also unticked. This isn’t gamebreaking, I can just tick the box in the part also… but it is a nuisance. So I was wondering if this was a bug, or if there is an obscure option like “always show ledger lines in part layouts” or something.
You may have simply encountered the difference between a local and global property. You can propagate the settings of properties from the full score to the parts.