To revisit this issue: the way enharmonic spelling works in Dorico is that if you change the enharmonic spelling of a note in the full score layout, that spelling applies not only to the full score but to all part layouts in which that note also appears, unless the note is explicitly respelled in one of those parts, in which case the spelling set in the part takes precedence over the spelling from the score. Enharmonic spelling is stored as a property of the note: although it is not a property you can edit in the Properties panel, behind the scenes that is exactly how it is stored.
Properties can apply either to all layouts, or to a specific layout, which is identified by the layout’s unique internal identifier. Enharmonic spelling in the full score is stored as a property that applies to all layouts. Enharmonic spelling in a part layout is stored as a property with reference to that specific part layout’s unique internal identifier.
When you copy and paste a note, its properties are copied with it. So if you copy a respelled note in the full score and paste it to another instrument in the full score, it will retain its edited spelling. If you copy a respelled note in the full score and paste it into another instrument in a part layout, it will retain its spelling in the full score, but it is not guaranteed to be spelled the way it was spelled in the full score in the part.
If you respell a note in a part, the spelling is stored in the properties for that note with a reference to that specific part layout. If you copy and paste a respelled note elsewhere in the same part, it will retain its edited spelling. But if you copy and paste that note to a different part layout, the spelling property will not match the unique identifier of the destination part layout, so that property will not be applied.
This is all very technical, I realise, but this is the fundamental way that Dorico allows you to have different values for the same property in different layouts, and what makes it possible to have as many degrees of freedom as you do when working with scores and parts in Dorico. The cost of that freedom, at the moment at least, is that some work has to be redone in different layouts.
In the future, we expect to have ways of influencing the way properties are propagated between layouts. However, in the specific case of copy and paste, we would have to take additional steps to try to decide which properties that have been set with one layout in mind should be translated when you paste to apply to the layout into which you’re pasting them.
I’m definitely not ruling out making changes in the area of translating layout-specific properties when copying and pasting at some point in the future, but we do not have any current plans to do this.