[MlMt] icon "double" clicking?

[Tracy Valleau]

I recently updated 10.15.4 with yesterday's "security" update. While I 
cannot say that's the reason, here's what I'm seeing today:

Using the trashcan icon* to delete an email deletes (moves to the trash) 
not only the selected email, but the one directly below it. Command Z 
returns them both to the inbox.

However, using the keyboard's delete key works properly, and only the 
single selected item is moved to the trash.

*actually, it's any button with an email selected. Trash, Archive, Junk 
- they all operate on the selected, and the following item.

It's almost like some kind of keystroke bounce: two clicks for the price 
of one. (That's not it, however: I checked.)

Is this happening to just me?  (versions 1.13.1 (5680 and 81)