What I expected to happen was...:
When I placed a piston facing a furnace and then powered the piston, the piston should push the furnace.
What actually happened:
The furnace didn't get pushed.
Steps to Reproduce:
1. Place a furnace on the ground
2. Place a piston facing the furnace next to the furnace.
3. Place a redstone torch next to the piston.
4. The piston doesn't move the furnace.

This is the same for all tile entities.
This is becuase when a block gets pushed it converts into a block that can't store extra data.