Sticky piston no longer sticking when redstone placed in a certain way

Bug involving sticky pistons' sticky power, video here :
http://www.youtube.com/watch?v=pGkLSKRK0g0

What I expected to happen was...:
piston to clock whatever i put on the side of the block

What actually happened was...:
when i put redstone one block away to the piston, it creates an impulsion and the sticky piston is no longer sticky.

Steps to Reproduce:
No need, I've put a video