Focus on wrong element when staging

[Broke dead dogg]

I don't know if this is a technical issue or my own incompetence.

I was launching a probe into orbit carrying some construction materials to my new space station, first stage, no problem, decouple of external fuel tanks also no problem, but when I stage for the third time I find my focus is still on the now expended twin boar engine while the probe with its poodle engine and payload shoot off into the distance.

And of course, I can't even switch because I'm still in the atmosphere!

Ive not had this problem before today and I've not changed the way I put my rockets together so I'm at a loss