Tnt minecarts behaving differently in 1.12

Stacking tnt minecarts and detonating them acts differently than previous versions (Don't know if it's intended or not because there isn't any specification on this)
– What i was expecting (and what happens in versions BEFORE 1.12):
When you stack multiple tnt minecarts into a single block and then detonate them by making them crash into a block, all the tnt minecarts are supposed to blow up ALL AT ONCE.
– What is happening (ONLY happens in 1.12):
When you stack multiple tnt minecarts into a single block and then detonate them by making them crash into a block, the tnt minecarts each detonate 1 by 1.
To create this :

• Place a rail
• Stack a couple of tnt minecarts on that rail
• Give the carts a slight push
• Then make them crash on a block
• Test on 1.12 and other version (other than 1.12)
• Compare