The batteries were fairly well-charged (better than 90%), so bulk charge rate shouldn't be a problem for very long. That's the odd part in that the charge load should not have been much more than the third or "float" level. All AC loads were turned off. No adaptor- the Honda 2000i is the "Companion" model with the 30A plug built in. I just connected it to the shorepower cord.
A stretch, maybe a polarity issue, or a GFI somewhere behind
the input plug of the shore power cord?