When you're plugged into shore power your inverter should not be providing AC. If it is it would be fighting shore power.
I'm guessing you popped the breaker in the house. As madeinchad said the converter would have been running charging the batteries and whatever else you had on. When the breaker popped, the inverter turned on (the transfer switch did it's thing). This caused your power to be momentarily off and your clock got reset (blinking). In the am you turned on the Keurig and the inverter stopped. Hopefully it's the output breaker on the inverter.