Entities floating and following entities/camera.

I was playing an adventure map on the latest snapshot, and during a 'boss' fight, signs and dropped items were floating around the screen, and would move with the 'boss' as well as with my camera.

I'm not sure how to reproduce precisely, but possibly:

Spawn a powerful mob (preferably with super speed).
Die.
Teleport somewhere nearby.
Entities should floating around.