Parts: set first selected instrument as default part title
when adding a new part (single part) the part title is set to "part".
It would be a good idea to replace this by the first selected instrument.
I often add an additional instrument to an existing score (with parts). So each time I need to set the part title explicitly. Or delete all parts and use "all parts" which sometimes is even easier (but means to loose all settings made before in the parts).