Recently, I experienced a strange situation with the Tektro hydro disc brakes on my hybrid bike (would the model be helpful here?):
I carried it upstairs at a friend's place, and later moved it downstairs by holding it upright and slowly pushing it downwards. When I started riding home, I noticed that the rear brake almost didn't react to any pull, I was able to pull the lever with minimum resistance until it almost hit the bar. I felt almost(?) no braking action. A few minutes into the ride, the brake fully recovered to the normal amount of resistance/braking force.
What happened here? What might cause such a behaviour? Could it be the bumpy ride down the stairs?
I never experienced fading on that brake so far, from the description it sounds very similar, though the brake was completely cool at the start of the ride.