When 3 running tnt minecarts hit each other, they explode without an activator rail

When 3 running tnt minecarts hit each other, they explode without an activator rail

What I expected to happen was...:
the tnt minecarts would act like normal minecarts

What actually happened was...:
They exploded

Steps to Reproduce:
1. Make a rail loop with at least one powered rail
2. Put 3 tnt minecarts on the rails
3. Push them until they all move (but they have to be moving in different directions)