Unlike lipo, NiMh has significant internal resistance (IR), so to charge NiMh, the charger has to stay at a higher voltage than the pack to be able to force amps into the battery and overcome this resistance.

It wouldn't surprise me to see over 10+v at the end of a 6cell packs charge. The voltage from the charger won't stop, since the voltage on the pack keep climbing, the charger has to keep raising the voltage to keep current flowing into the battery.

Charging a NiMh requires a diff charger response than what is required in charging a lipo.