Piston Still Powered with redstone block and removing redstone lamp

The Bug / How To
If you spawn a Piston and put a Redstone Block on it (piston effect side) nothing will happens .
If you now put a redstone lamp near by the piston to power it and remove it then the Piston will Still be Powered on !
IMPORTANT: The Piston Effect side must be UPSIDE (else it wont work) .

Screen:
( 1. How to Build . 2. Normal Look 3. The Bug )