MPPT SmartSolar Load Output can't turn On if Load already has voltage

I have a MPPT SmartSolar 100/20.

It works great, except I can't figure out the Load output.

Using the app, I set the load output to "Always On" or "Always Off".

If I test wtih nothing connected to the Load output, it works as expected: When set "Off", voltage drops to zero, as expected. When set "On", battery Voltage appears on the Load Output + terminal.

If I then plug in the load, it shows a 10 to 15amp draw, which is well within the capacity of the device (20 amps).

However, if I leave the load connected, and then set it "On": the app shows the load is "On", but shows 0.0 amps flowing (which I've verified with my meter).

The load in this case is another battery, so it's sitting at around 12.0 volts.

It appears that this is causing the SmartSolar to get confused, and therefore the load output will only turn on if there is no voltage at the load output + terminal.

The pattern is repeatable: as long as the SmartSolar load is turned on before I connect the load, it works fine. Otherwise, it seems to get stuck in the "On, but zero amps" state.

Is this how it's supposed to work, or is this a bug?