The following change has some annoying side-effect:
2005-12-10 Kevin Rodgers <address@hidden>
* emacs-lisp/lisp.el (lisp-complete-symbol): Regenerate the
completion list, even after a partial completion has been
inserted in the current buffer. If there are more than 1
completion, redisplay the *Completions* buffer; if the
completion is unique, delete the *Completions* window.
The problem is that it changed the behavior such that the *completions*
buffer is shown after every completion. Before that change, the
*completions* buffer was only shown if the completion failed because
of ambiguity.
I'm not sure what this was supposed to fix, but I think it was not the right
fix,