In shell-mode, should *Completions* buffer disappear after completion?

[William Brower]

With M-x find-file, after a sucessful completion in the modeline
with <TAB>, and acknowledgment with <RETURN>, the temporary
*Completions* window which splits my frame disappears leaving
me with my single one window frame. That's the good news.

The same behavior does not occur when in shell-mode.
That is, in shell-mode, hitting <TAB> at the command
prompt correctly opens a *Completions* buffer in a
new window within my frame (i.e. my frame is split)
but upon sucessful completion (the modeline even says so),
the *Completions* buffer remains and my frame remains split.
Is this because there is no "acknowledgement" phase as with
Mx- find-file?

Or is this a bug? Is it configurable behavior? A feature?

Thanks,
Bill

-- 
William Brower  MIT Lincoln Laboratory
805.355.1310    KMR Field Site, Kwajalein