I don't think the breaker in a grid tied system is truly "backfed" since the utility has to be present on the "line" side for the inverter to put out. (which will power the breaker circuitry).
I agree if you are truly backfeeding, like on a generator inlet, you will smoke them but that is not what is happening on a grid tie inverter.
The idea that net current is flowing one way or the other is meaningless since the current switches direction every 8MS anyway. The CT only makes sure they balance.
You are kidding right?
