What I expected to happen was...:
When i trigger a TNT minecart with a activator rail, the block below the powered rail (not considering the one that the rail is on) are supposed to stay intact, since the block that the rail is on acts as a shielding block and damage isn't supposed to go trough it (like a obsidian block)

What actually happened was...:
when i trigger the TNT minecart with a activator rail, the block below the powered rail (not considering the one that the rail is on) get destroyed, same goes when you surround the TNT minecart with blocks WITH rails on top of them (as trying to create a controlled explosion), damage goes through those blocks and destroy the block, within range, that don't have a rail on them.

Steps to Reproduce:
1. Build a platform (ANY block, considering even obsidian and bedrock) a few block in the air.
2. Place any type of rails on those blocks (exept 1 activator rail on which we are gonna place 1-5 TNT minecarts)
3. Build a other platform (made of breakable blocks : Avoid obsidian and bedrock) 2 blocks below the first one.
4. Power the activator rail that will ignite the TNT minecarts.
5. The second platform will get destroyed by the damage.