1.       Exactly what I did

I created an entry in an org file.

I added an attachment to that entry.

I used refile (C-c C-w) to move the entry to another org file.

I visited that file and attempted to open the attachment (C-c C-a o).

2.       What I expected:

Because there was only one attachment associated with the entry, I expected
it to open.

3.       What happened instead:

I was prompted for an attachment name. Hitting <tab> showed "no match" in
the minibuffer.