Dropped item becomes invisible when pushed by piston

Steps to Reproduce: 

1. Place a sticky piston on the ground facing UP.
2. Place a block of dirt on top of the piston.
3. Drop something on top of the dirt-block.(example: gold)
4. Active/Deactive the piston using a lever.

Observed Results: 

1. Activate the piston >> dirt moves UP >> gold falls down.
2. Deactive the piston >>dirt moves DOWN >> gold is on top of the dirt block.

NOTE: 

When the gold falls in the ground, I can see it in the ground but actually the gold is on top of the Dirt-Block.