In a particular type of document I like to put in separators between
sections like this:

---------------------

For some reason, Word then decides that I want it to put in a horizontal
line, and puts in an additional line like this:

__________________________________________________________

So I now have something like this:

__________________________________________________________
----------------------

And then, once this has started, Word starts throwing these same lines in
every once in awhile at seemingly random places, even if I do not put in a
series of hyphens.

Why is it doing this, and how do I stop it?

Thanks,
Scott Kelley