It's just the battery driver and the way the battery percentage is reported...

The battery meter is just a voltage meter, nothing more.

100% charged is 4.2 volts... The battery will stay at 4.2 volts as long as the 5v from the charger is applied... naturally, when you remove the 5v charge, the battery voltage will drop some...

The voltage drops from its cutoff at 4.2v and this "decrease in the battery" is what you see when this happens. This is a normal phenomenon and the only real fix is to adjust how the voltages are translated into percentages... right now it's just a straight line correlation from 4.2v being 100% to uhh... 3.5v i think being dead? I'm not exactly sure what the low voltage cutoff is.

If we adjusted it to be a bit of a curve, where 4.12-4.2 volts would show as 100% when removed from the charger, you'd see it stay at 100% a little longer.