I used to be able to highlight a block of text and then hit "backspace"
(instead of delete) to remove the text. Now, when I highlight text and hit
backspace, it places the cursor at the beginning of the (now unhighlighted)
text.

It doesn't do this for any other application (except Outlook which uses Word
as its editor).

I've tried various combinations of insert and delete to see if this is a
toggle issue, but to no avail.