re: "If there is an imbalance that means current IS flowing in the ground circuit."
That may be true, but that is not what casues a GFCI to trip.
Your original statement was "The GFCI breaker works by detecting leakage current on the ground wire" and that is the only point I am arguing.
Your statement implies that the device is monitoring the current on the ground wire (how else would it detect the current?) and when it detects the leakage current it trips.
You may call it semantics, but I call it science. The fact remains that your statement "The GFCI breaker works by detecting leakage current on the ground wire" is just plain wrong, regardless of how you try to justify it. I'll even give you some latitude and let you leave off the word "wire". The fact remains that the GFCI doesn't detect to leakage current on any type of ground circuit. Period.
It works by detecting the imbalance between the hot and neutral wires. Regardless of where the leakage current is going to, that leakage current itself is not "detected" by the GFCI. It is the *imbalance* between the hot and neutral that is detected.
Compare it to pressure-balancing in a shower valve. The valve itself will sense the difference in pressure (substitute: current) between the hot and the cold (substitute: neutral) and adjust itself to maintain the original balance (substitute: trip).
It doesn't "detect" the cold water flowing through the pipe (substitute: ground wire) to a toilet or a washer or a sink. All it knows is that there is an imbalance right at it's point of monitoring and it compensates for it.
That's how a GFCI works. Look it up.