Completion problems - completion window not rewritten

[Lennart Borgman]

Start with

  emacs -Q

In the *scratch* buffer enter the text

  'default-

and the type

   ESC TAB

This gives all completions for default-* in the *Completions* buffer. 
Now continue to type so that the *scratch* buffer contains

  'default-dir

Again type

   ESC TAB

I would expect the *Completion* buffer to show only the now useful 
alternatives. However this does not happen. Closing the window showing 
the *Completion* buffer and trying again with ESC TAB shows the correct 
alternatives however.