So you disappear from the screen for 3 seconds. So what? They knew who and where you were, they told you to change squawk so if you drop off the screen (if the primary is that poor) for an instant before popping back up in another guise it is hardly a surprise to ATC, is it?
That argument sounds perilously like cobblers to me. I'd be far more concerned by accidentally passing 7*00 and setting off all the alarms, so I'll continue to select SBY before changing squawk as good airmanship seems to require.
Whats the problem with that?