I doubt it matters. The power company also theoretically has to deal with houses where they coincidentally draw more from one side of the split than the other. But I suspect it all averages out, and the contribution of a couple plug-in panels in a bunch of houses won't change anything.

U.S. homes typically get power through two hot wires. The hot wires are connected to a utility company's transformer and are 180 degree out of phase. Each supplies 120 volts.

The power from the plug-in outlet is consumed by any devices connected on the same circuit first. Any extra flow through the electric panel’s bar connecting the circuits on the same 120V phase, where the devices on them use the extra next. Any excessive power flows back out of the meter on the 120V phase line on your service connection to the transformer at the street block. The transformer might feed it to your neighbors. In any case the transformer feed electricity to the other 120V phase line back into your service connection, the meter, the panel, the other split phase bar, the circuits on it, and the outlets on them. The devices on the other split phase circuits technically are not using the plug-in power directly.

Most modern meters measure electricity going in and out on both split phase lines as a whole, as a net amount, so the electricity consumed in the other split phase circuits is offset by the plug-in power. However some old meters add the outgoing electricity up as consumption so you are paying for the electricity fed into the grid. Call your utility company to make sure.

Also, unless you have a net metering agreement with your utility company, you won’t get paid for any excessive electricity fed back into the grid.

There is no problem and so nothing needs to account for it. A split phase is just a transformer with three windings, and one is connected to the other. We call one side (high voltage) the primary, and the other two secondary, but the transformer doesn't care at all, it can send power either way (there are limits but we are well under the maximum rating of the transformer so we can ignore them). If you only draw 240 volts then the two connected windings act as a single secondary, if you only draw 120 then one of the two secondaries provides power. Any other combination - the transformer doesn't care.

It backfeeds onto the grid and becomes the utility companies problem to deal with. This is similar to them dealing with a house that is an unbalanced consumer between the legs.