It just happened again. I'm going to post my "fix" for it.
And thank you @PinkElephantand @agsteelefor the tips. The F11 didn't work, although it sounded like it had a good chance.
If you go to Edit/Search notes from the menu, it magically fixes itself.
Like I said above, it doesn't happen all the time, but when it does, it was when I was searching.
I don't think it's worth a ticket, but maybe the Evernote developers (or product owners) watch these conversations and will put it on a "maybe someday fix this tiny bug" list.
Thanks again!