redstone mechanic bug

Put the summary of the bug you're having here

What I expected to happen was...:
i thought the piston is gonna retract

What actually happened was...:
it did not

Steps to Reproduce:
1. this require a window 7 with 4 GB memory
2. make a piston door like the layout

sand(any material)

pressure plate

piston-redstone-redstone-redstone torch on a block

redstone

redstone-redstone-redstone-redstone-connect those 

redstone to the block the torch are in
3. you can see that the door doesnt open