The company says the problem happens as the car switches from a regenerative braking system, mean to help recharge the hybrid's batteries, to conventional hydraulic braking, The Detroit Free Press reported.
The cars "maintain full braking capability," Ford said, but drivers "may initially perceive the condition as a loss of brakes."
The brakes don't actually fail, says David Champion, director of automobile testing for Consumer Reports, but the pedal drops and drivers might think they've failed.
Though he views the brake defect as scary and serious, Champion noted that Consumer Reports has praised the overall quality and safety of the Fusion Hybrid, the Free Press said.
About 18,000 Ford Fusion and Mercury Milan Hybrids might be affected by the electronic brake-software glitch, Consumer Reports said.
A similar occurrence is being reported with Toyota's hybrid, the Prius.
Copyright 2010 United Press International, Inc. (UPI).