Piston Bug

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here
I made a semi-auto sugar cane farm and it works.

What actually happened was...:
Describe what happened here
for some reason the top 4 pistons create a fake extended piston block.

Steps to Reproduce:
1. make what is in the attached screenshot and press a button that will invert the inverted signal
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