Sand ghost blocks using pistons

Put the summary of the bug you're having here
When moving sand and gravel with slime blocks on pistons connected to a redstone loop, it creates more sand/gravel (client side only).

What I expected to happen was...:
The sand/gravel move up and down with the slimesblock.

What actually happened was...:
It duplicated the sand and gravel for the client only (ghost blocks).

Steps to Reproduce:
1. Make a arrangement of pistons, sticky pistons and sand or gravel as shown in this image http://imgur.com/CRry1jj.
2. Create redstone loop using a comparator, redstone dust and a lever, connect to the sticky pistons.
3. Watch the sand "duplicate".