Lee
I know what you mean about it bugging you. If you have all the AC breakers off the only source for the power is from the inverter and batteries. What happens when you have the bus AC breakers on and the CG power plugged in? I am quessing that when you say AC breakers off you mean the ones in the buses main electrical panel.

I doubt your problem is with the transfer switches in the inverters, it is very unlikely for both of them to be bad and not passing AC thru.

In order for you to have power to the bus you have to have the buses AC breakers on, unless Liberty is really wired different.

The other thing you can do carefully is check for voltage coming out of the buses transfer switches and work towards the inverters, both input AC and output AC.

GregM