Word suddenly displaying all formatting!

[Matthew W. I. Dunn]

I go to the head of the text (unindented; anywhere in the document). I press
SHIFT and a letter to insert a capital letter.

Suddenly -- and, for no reason that I can think of -- all the formatting in
the text is displayed. So, I go Office Button > Options > Display and see
that "Show all formatting marks" is now checked. That clears up the
formatting.

But, when I hit Backspace to delete the capital letter I inserted (after
which everything went screwy!), the cursor will not go back any further or
delete. I have to skip before the letter, press Delete, in order to delete
it.

I just ran Diagnostic yesterday evening . . . and, this is happening.
Something's wrong with this product!