The programs vary. I've attached an example, two screenshots, of two programs needing updates checked, but afterwards only one was updated and the other is now unchecked. This happens every time when there are two or more, no matter which programs are involved.
The other thing I'm unclear about is why I have to check items on the left, i.e., why I can't just use Perform updates box at the bottom right. I was using that alone until I decided not to update one program for awhile (now updated). Since then, I've always had to check items on the left, which exposed the issue I'm raising with this post.