git branch -D doesn't work with deleted worktree

Git 2.11.0 gives a wrong error message after the following commands:
 
$ git init
$ echo hello >file
$ git add file
$ git commit -m "message"
$ git worktree add ../worktree
$ rm -rf ../worktree
$ git br -D worktree
error: Cannot delete branch 'worktree' checked out at '../worktree'

Since ../worktree has been deleted, there cannot be anything checked out at that location.

In my opinion, deleting the branch should just work. Especially since I used the -D option and the "git worktree" documentation says "When you are done with a linked working tree you can simply delete it."

Regards, Roland