Never, ever, go Stby in the air when putting in a new squack.
I did that on departure long time ago, had a rather close call!
Trust me on this one!
Not smart!
Tcas dont work and on Radar you vanish!!
( I had the wrong squack, that was what started it all, long story, short answer: NO stby in the air.)
High on my Top 10 never again list!!