This could be for one of two reasons. The suds screen and/or foam sponge are not in place. If not in place, this would allow too much water to dispense, over-wetting your carpet.
Repeatedly cleaning the same area would also cause this. To avoid over-wetting moving forward, allow the system to dispense a layer of foam on the carpet and then turn the valve on the shampoo tank to OFF before going back over the area to work in the foam and scrub the carpet.