It still happens, i've uploaded another three pictures which show the
problem more clearly

In step1.png it has no problem. Then i typed C-x } *once* to make the right
window narrower, as in step2.png
Then when i tried M-x align<TAB> the problem occured, after i typed another
<TAB> Emacs has no responses.
Additionally, when i have two of emacs running in this situation, the system
becomes really slow, since emacs consumes nearly 100% CPU

On Mon, Mar 30, 2009 at 1:21 AM, Chong Yidong <cyd@stupidchicken.com> wrote:

> > I opened two windows using C-x 3, and set the width of the right
> > windows to a really small value (to be more precisely, it can display
> > 50 characters per line). Then on the left line I run some command like
> > M-x align<TAB>, as a result, the right window will be used as
> > minibuffer and display auto-completion list. The bug is that, the list
> > comes with all '\' on the right most and just cannot stop printing,
> > and does not response to my control. In program 'top' I can see the
> > CPU% of this emacs process is 100%.
>
> I can't reproduce this.  Does it happen with `emacs -Q'?
>