completions - remove window after use?

[David Reitter]

When showing a *completions* buffer in a new window opened for it (TAB in 
find-file minibuffer for instance), I wonder why the window doesn't get deleted 
when completion has finished.  For instance, when an existing file is found, 
the *Completions* buffer is buried, but I see a split frame with the original 
buffer in the top window and _some other_ buffer in the lower window.

Shouldn't the window for the completions buffer be removed whenever it has been 
popped up just for the buffer?