The cells will rebound as they are removed from a load. So your 4s pack is probably hitting the cutoff under a load, and rebounding to whatever your charger reads.
Though ACCURATE? My eagletree elogger confirms that my MMM is letting my packs go about 0.8 volts lower than what set it at.
Check out my custom converted 8ight:
Sub 7lb, lowest CG of any 1/8 buggy