Brake Sensor problems of the 2012 Lincoln Mkz Hybrid

Traveling south on ct15 in stop and go traffic. Traffic was moving at about 40 mph and stopped suddenly. I applied presuure to brake pedal to stop. Pedal went to floor. It appeared that minimual regenerative braking was engaged but no additional friction braking. Car had plenty of distance in which to stop [ more than 140 feet]. Car slowed for a time but when speed was reduced to about 10 mph, the regenerative braking disengaged and car surged forward and rear ended truck causing substantial body damage. No warning lights were lite on dash. Dealers had inspected brake both before and after crash and reported no problems. Simulated brake assist did not provide any resistance to pressure on pedal. Brake pedal position sensor did not generate brake request or abs and ecm did not recongnize request for extra braking. Extreme pressure on brake pedal did not activate fail/safe manual friction braking. Car should stop in 140 feet from 60 mph. Questions - what was the cause of the sba not activating? why did the abs and ecm ignore or not properly respond to the braking request? why the fail/safe friction braking mode fail to activate? what pedal pressure is required to activate mode? there are numerous prior reports of similar symptoms causing accidents in 2011/2012 Lincoln/Ford hybrids. What is the stopping distance from 60 mph in fail/safe mode. Ford literature on the hybrid braking system does not speak to this issue or give any warning to customers. How is the fail/safe friction braking system tested to insure proper operation in an emergency? why does the brake pedal go to the floor when driver is attempting a panic stop?.