It's not a bug but simply the way the charge display has been configured by Palm.
If you charge long enough, the display will eventually show 100% - while the Centro is being charged.
The moment you disconnect the charger, the display will change to 99%.
I like this much better than what Palm did on the T3 (I've had four, and all behaved the same way):
You'd charge up to 100%, the display would stay at that value for half an hour or more, and then, in the blink of an eye, drop to 83%.
Regards,
Jochen