Alan,
I have finally figured something out.
On a few occasions lately, there appeared to be no cursor on my screen. I pulled it back in from off to the right. I wondered why it took so long to come out of the right edge of the screen. Somehow, presumably as a result of the recent updates, I have a second screen off to the right of the one I am viewing, and the mouse cursor was lurking over there.
So, Printscreen was doing its job OK, when I clicked to save a screen, that's what it was doing, saving BOTH of them.
So, now I get to the point of needing to eliminate the unwanted second screen to the right.