Curious, never had that with my normal BC6... Try charging the packs at a slightly lower current maybe so that the cells can even out more durig the charge, or, if you cycle through the display towards the end of the charge (~1 hour assuming a 1c charge rate), take a look at the individual cell voltages. If they are all 4.19-4.2v and staying there pretty much, just stop the charge manually; just check the mah thats been pumped back in, should be about 80-90% of the packs rated capacity.
As for the real reason for the problem... pass