Patch tool does not replace selection

I'm using PS release 22.0.0.  I'm having a problem I've never had before with the patch tool. 

This image provides an example: Just a single layer.  If I select with the patch tool in the yellow box (source) and drag to the blue circle (destination), a blue area appears in the yellow box, as expected.  However, when I release the mouse, nothing happens.  Doesn't matter whether I use Normal or Content Aware. Resetting Preferences doesn't fix the problem.  Any suggestions?