Now that I think of it... It might be a bug with the fuse tag.
Exact command for TNT summoner command block:
/summon PrimedTnt ~ ~8 ~ {fuse:3}
First a command block with
/testfor @e[type=Arrow,r=50] {inGround=1b}
sets off a comparator that powers a command block with
/tp @e[type=PrimedTnt,r=15] @e[type=Arrow,r=50]
Everything is typed perfectly as far as I can see... And I can see the comparator from the arrow in ground command block turning on and powering the tp command block.
Confirmed