Yeah, LiPo's aren't supposed to be trickle charged anyway. I'm not sure about this charger, but some do keep checking to see if a charge can be taken. In reality, it's just the topping off stage of LiPo charging. I've had cases where a customer's (supposedly fully charged) battery wouldn't last long in flight. But, leaving the battery connected to the charger for 5 or 6 hours cured it and the battery continued to charge fine and run normally afterward.

Briefly - LiPo used a complex charging method know as cc/cv (constant current/constant voltage). The cc stage is actually pretty fast. The cv stage takes quite a bit longer. The max. charge or 4.2v can be reached quickly, but stopping the there could mean the battery only has about 70% full charge. The cc stage may last until the rate drops below .03C. That may be 4.1v, for example, then it's switched to cv which charges the battery with close tolerances (+ or - 50mv) to a full charge of 4.2 or 4.22v (whichever is specified in that charger). This is a slow stage so the battery won't overheat.

For our AA purposes, charge until the light goes out and you'll be all set. If your battery doesn't seem to hold a charge as well as it should, and it's not real old (like 250 charge cycles), you could try leaving it on the charger for 5 or 6 hours and see if it helps. The charger may rest of a couple of hours and then resume the topping off stage.