Sometimes PrimedTnt entities seem to just disappear. Try setting of TNT a few times, every now and then it just disappears and never comes back...
Comments 2
https://www.youtube.com/watch?v=VHC6SpMsEkI&feature=youtu.be
Unfortunately, I can reproduce about 50% of the time. Seems to only happen in flowing water...
Cannot Reproduce
http://i.imgur.com/0VpWP52.jpg