Are you using the OEM charger? I don't know have this problem a C6906 on the OEM charger (and my SGS2 charger, actually). Try charging it from a different source. When the battery reaches 100%, the charger might back off too much and let the battery drain a bit, leading to an endless loop.
It could also be software weirdness (tough to tell with some of these problems). Try doing a factory reset if changing the charger doesn't help.