Can't add notes to one voice. Notes in last measure have gray heads

I searched through the forums and couldn't find this. I'm a new user, so it may be something dumb on my part.

I'm creating a score with three voices/staves using Version 1.3. I pre-set the score to 84 measures, then as I wrote it, I turned on the option to combine rest measures for 3 or more rests.

I entered parts on all three staves, and when I'd get to the end where the combined measures were, entering notes there would expand into a non-rest measure as expected.

Somehow, when I went to enter notes on the third staff, the last measure notes have gray heads. When I try to enter notes on that staff, the cursor shows a tiny note head and I can't paste to that stave, but i can to the first and second.

Did I somehow corrupt the file, and is there a neans to recover without re-entering everything?

I have attached screen shots depicting the above. Thanks for any help you can provide!