TNT Cart doesn't save

I was playing around with the TNT Cart and when I saved the world and returned it wasn't there anymore.
How to reproduce:
1. Place a TNT Cart on a rail
2. Save the word
3. Open it again
4. The cart is not there anymore or is not rendering at least

EDIT: After looking at it in NBTExplorer, I can confirm that it is not being saved at all.