You can create a line by holding down the equal sign or the hyphen for a few
characters, the system automatically creates a horizontal line. That's
great, until you want to delete it. It won't delete easily, and on a label
it won't delete at all. All the words will delete above and below it, but
you can't delete the line itself.

Version: MS Word 2000

This appears to be another example of MS Word assuming you want something
and making it difficult to get what you really want. Dang that is annoying.
Help seems to have no knowledge of that feature either. They should
de-implement that auto line making feature -- people can hold down the equal
sign key pretty easily all by themselves.