Low Power Inverter Imports Energy?
Alright, so this isn't really an EE anomaly as much as a metering issue. What's happened is the meter we're using has two accumulated energy measurement fields. The first is Total kWh, which measures all energy in either direction flowing through the meter. The second is Reverse kWh, measuring the energy flowing out from the load (production). The meter doesn't measure, but only calculates Forward kWh, with the formula Forward = Total - Reverse. That alone seems weird to me. Why not just measure forward and reverse? Who cares about total?

But this problem appears because, due to rounding, sometimes Reverse increments w/o also incrementing Total. This causes the calculated Forward to decrement, screwing up the readings. Eventually, Total will increment w/o incrementing Reverse, "correcting" the problem, but also causing Forward to increment incorrectly. 

TLDR: Know how your submeter works very well before installing.