It detects shore power and I mistakenly presumed it would detect a load as well. Apparently not!
I am not sure what you mean. The Victron, and all other reputable marine
inverter/chargers that are wired in the AC panel supply do work this way. The I/C analyzes the incoming voltage, frequency and waveform and, if "qualified", passes the incoming power through the I/C to the AC panel. A portion of the "qualified" incoming power is utilized by the charger
portion of the I/C to charge the connected batteries.
If the I/C controls are aligned so that the inverter
portion of the I/C is in standby, loss of the incoming power, whether from shore power
or the genset, will instantly shift the I/C from pass through and charging
to inverting. This transfer typically happens in a few msec and a powered load will not experience any loss of power.
The Victron Multi Plus and the Quattro are very sophisticated and actually stay in synch (voltage, frequency and wave form) with incoming power and can be used to boost the power from an undersized generator
or substandard shore power pedestal
when starting large loads.
Hope this helps.