Mining a cart does not drop the cart item

My world is experiencing the famous "mining a minecart won't drop the cart item" bug. It happened once before and it seemed to have sorted itself out very quickly, but now it's back and it seems persistent. 

In survival mode: 

1. Spawn into the world as an owner (it's a survival world).
3. Place down a minetrack anywhere. 
4. Place a minecart on the mine track. 
5. Use any tool to mine the cart. 
5A. Cart goes poof. Doesn't drop. Doesn't show up in inventory. 
6. Cart doesn't show up hours later. I've mined several carts in the same place and they're all still gone.