Duplicate player adds the new one to all existing layouts

First things first: I only have one single file that exposes this weird behaviour, so this does not affect everyone.

When I select one single player in setup mode and do “Right click > Duplicate player”, the new player gets added to each and every existing layout, creating quite a mess.
Has anybody ever heard of this?

I will send the file to @dspreadbury, as it reproducibly exposes this in this file. I immediately tested it on another file, but everything is ok there.

Edit: This is a native Dorico file, no XML-import.

It should get added to every Score layout, but not Part Layouts.

Yeah, that would make sense.
But it really is each and every layout that is beeing affected. I have “Flute 1 + Trumpet 4”, “Trombone 2 + Trumpet 4”, and so on.
And it does not matter what “kind” of player I duplicated. Brass, percussion, you name it.