Thank you for the explanation, I understand. At this point I'd like Adobe to rethink this intentional design as it is illogical from the user perspective and I'll give 2 examples.
1) The spot healing brush tool does not work like this. Select the heal tool and remove an object. Then hit "undo". The object returns, but the tool stays active, ready to be used again. Same for the red-eye tool. Also the same in Photoshop. Select nearly any tool in PS (heal, marquee, selector, brush, burn, clone, etc.) and then do something. Hit Undo, tool stays active, ready to be used again.
2) Imagine a painter, in real life, who has a Magic Remote Control. She goes to the cupboard and gets out all of her paints and painting tools, She gets them set up and gets ready to paint. Then she paints her first brush stroke on the canvas. She decides it was a mistake and wants to wipe clean that single brush stroke, so she activates her Magic Remote to Undo. Poof, all of her paints and brushes disappear back into the closet and she has to go through the setup process all over again.
I know that Adobe works hard to do a great job of understanding the very efficient workflow of full-time professionals who use the tools everyday. Fewest clicks possible is always the goal, logical efficiency. This new brush function has added and extra click in this situation, an extra step that did not exist before, and also does not act the same way as other tools in the PS ecosystem.
And so I ask for change, when we hit the UNDO button to remove a brush stroke, the tool should remain active and ready to move forward. Thank you.
I'd be totally in favor of changing the Undo behavior for the Brush when it is the first and only component in a mask. This has happened to me way too many times, exactly like the OP describes it: I start a new brush with the K key and after I made the first brush stroke realize that I had the wrong brush active (A instead of B), the flow was too strong, the feather wasn't right, whatever... I hit CTRL-Z and then have to go back to K and begin with a new brush again; it doesn't seem logical.