David Friggens writes:
> > What mode was the buffer in (c-mode)?  Might you have been in
> > text/fly-spell or something similar?
> No, I was in Prolog mode this time.
> It's happened in other modes (but not c-mode, from memory).

You realize that in prolog mode the TAB key is not bound to
self-insert-command?  It runs prolog-indent-line, which inserts as
much space as it feels like (according to some indent algorithm).

If you want to forcefully insert an ascii "TAB" you want to type "C-q
TAB".

Now why prolog mode and you disagree on the indenting is another
question.  In general emacs' syntax parser is very weak in correctly
identifying whether you are in a string or not.  Perl mode tends to
get totally confused with things along the lines of: 

	    \" 

	    (or)

	    # 'tis a random comment

	    (these are from memory, so I may have the details slightly
	    wrong.)

Could the same sort of thing be happening to you in prolog mode?  Does
TAB still work at the top of the buffer, but stop somewhere lower
down?

-wolfgang
-- 
Wolfgang Rupprecht    <wolfgang@wsrcc.com>     http://www.wsrcc.com/wolfgang/
Coming soon: GPS mapping tools for Open Systems. http://www.gnomad-mapping.com/