Backspace randomly starts deleting bullets...

I write a lot of lecture outlines in MS Word using bullets. It works
extremely well, however, the funniest thing happens and I'd love to be able
to stop it.

Everything will work great for a time:

When I press tab, the bullet will indent one tab forward.
When I press backspace, the bullet will de-indent one tab backward.

.... then, all of the sudden, without any purposeful doing on my part:

When I press tab, the bullet will indent one tab forward.
However, when I press backspace, it deletes the bullet.

.... and this continues for the rest of the document and I can't seem to
resolve it (i.e. get it to go back to de-indenting my bullet instead of
deleting it when I press back space).

If anybody could offer up any solution to this, it would mean a great deal.

Thank you kindly.
--
Robert Grunwald, MD, PhD
Department of Neurological Oncology
David Geffen School of Medicine
University of California, Los Angeles