>>>> "Stephen J. Turnbull"
<stephen(a)xemacs.org>: 
 I don't understand why C-g doesn't help, but it is known
that
 there's a bug in the regexp code.  You can work around it by using
 21.4.15, 
Not really an option for me, since I don't build XEmacs myself.  I
just apt-get it.
One thing I can do, is to use debian's non-mule version of XEmacs.
Appearently the problem isn't present there.
 but that will break all regexps that use shy groups---they will fail
 to match correctly.  The cause of the bug is unknown at this point. 
An article in posted to ding(a)gnus.org, mentions a fix applied to the
official freebsd port:
	
http://article.gmane.org/gmane.emacs.gnus.general/59500
I've no opinion on this patch's validity.