Way 1: Placing a tnt cart on a rail, then destroying the rail makes it stay where it is. Pushing it around does not make it explode.
Way 2: By pushing it through a block with this setup:
https://www.dropbox.com/s/u7w2ni3nfpls35c/2013-02-15_00.11.07.png
Just place a tnt cart on the diagonal rail, wait a second and place another 1.
Then wait untill the second cart pushes the first one all the way through the block and you can start pushing it around.
Duplicate of MC-6858 and MC-8004, please use the search function to see if your bug has already been submitted. Currently over 51% of tickets are being closed as duplicate.