I have the 2554 06 model, which does the same thing. I first thought it was the exhaust, but that points straight out the front of the tractor. I believe it is just the heat off the engine and with the hood closed between the pulleys and probably the fly wheel directs all that heated air too the grass. I have put my hand under the tractor after cutting 1.5 acres with it running and it is plenty hot.
I lifted the hood and it seemed to relieve the air direction traveling to the grass. But I have not tried to see if the grass still got burned. Most of the time I just shut it off if I get off the tractor, or if cleaning the mower deck with the deck wash I do it on the driveway.