Piston Extender With Slimeblock Duplicates Redstone Block In Water

Video prove:
http://youtu.be/RFGZXfO93Us

What I expected to happen was it will clear out the ocean in creative mode.

What actually happened was it duplicates the redstone block that was bud powering it.

Steps to Reproduce:
1. Place 1 row of sticky piston (about 3 in length).
2. Place a row of slimeblock (about 8 in length).
3. Place another row of sticky piston facing the slimeblock.
4. Place a row of redstone block on top of the slimeblock (length same as piston).
5. Slowly destroy the slimeblock and update one of the piston every other second.

The structure needs to be built on water or in water.