Xcode moves *.playground/ folder?

I have a playground ~/Rope.playground/ and associates sources under
~/Rope.playground/Sources/. Xcode frequently creates new folders,
~/Rope.playground/ and ~/Rope.playground/Sources/, copies my .swift
files there, and then deletes the originals. This plays havoc with my
editing the source files with vim.

Any ideas why Xcode does this and how/whether I can stop it?

I have only noticed this happening in a playground. Xcode otherwise
seems to cooperate pretty well with an external editor.

Dave