[BrianG]

Actually, that's normal. What you did was put enough current back in the cell (and it takes very little to do this) to bounce the voltage back up to the cells rated voltage. Sometime, put a pack on a discharger and watch the voltage as it gets near 0.9v/cell. Once it gets at or a little below that, the voltage will drop VERY quickly.. like falling off a cliff quickly.

Your motor spun up fast because a single unloaded motor doesn't have much load, so there is little current. If you were to somehow load the motor, you'd hear the motor slow down really quick.

That said, I would charge the pack slowly to recondition them. If possible, do each cell seperately n case you have several bad cells. Then I'd do a few charge/discharge cycles on the whole pack to get it back up to par. For the whole pack to be that low means it was probably stored for a long time almost depleted. Also, charging heavy currents in a pack that low can cause cell reversal (bad).

EDIT: GD beat me to it.