Same findings while braking using 10s1p A123, Jazz 55-10-32 and a Neu 1512/2Y in a 11lbs truggy.
Here is a graph of 3 accelerations and brakings.
The green curve shows motor RPM.
-> Voltage rose between 1-1.5V while braking
-> Amps spiked at below 20A while braking