I think I have a similar problem.
Yesterday I trickle charged my 2015 Leaf S for about 8 hours with Leaf Spy Pro running on my phone and a bluetooth transmitter connected to the OBD port. When the car was about 70% charged, I attempted to back it out of my garage and down an inclined driveway.
It was a fast, scary blur, but I think that the brakes did nothing--I do recall a clicking or grinding sound--and I stopped the car with the parking/emergency brake. I sat there, dazed, and assumed that I hadn't actually put the car into drive mode, so I tried it again--with the same result. I was able to stop the car from rolling backwards by putting into D, but then the car continued to creep forward, and the brake pedal seemed to be ineffective. I quickly applied the parking brake and shut the car off.
At about 5AM the next day (today), I checked the car again. The following warning lights ARE on: brake warning (both "BRAKE" and the drum brake symbol with the exclamation point in the middle), ABS and the master warning lights (both red and yellow). However, Leaf Spy Pro indicates NO Diagnostic Trouble Codes.
Regardless of the outcome, I HAVE already filed a report with NHTSA at https://www-odi.nhtsa.dot.gov/VehicleComplaint/
(This could be a SERIOUS problem.)
Perhaps coincidently, my local Nissan dealer "reprogram[med the] electrically-driven intelligent brake control unit" about 5 days ago. This was per a Nissan recall, I think. (My invoice indicates "PERFORM CAMPAIGN P5327.") There is another thread for P5327: http://www.mynissanleaf.com/viewtopic.php?f=27&t=20785
This happened about 7PM on a Sunday night, so I'm waiting to call my local Nissan dealer and/or the Nissan 800 number at the start of the business day on Monday.