tnt in minecart doesnt blow up rail and the block its on

I was testing out the new released to see what was new and tested out the mincart with tnt. but when i did i blew it up and noticed the floor underneath it had stayed there where it blew up. i thought it was some lag so i did it again to see if it was or not. it still didnt blow up. so i planted normal tnt next to it and it blew it up.

Its not a good picture but it is the best i could do