Piston doesn't retire after powering off the redstone signal

Put the summary of the bug you're having here

What I expected to happen was...:

all pistons retiring after powering off the redstone signal

What actually happened was...:
the first piston didn't retire

Steps to Reproduce:
1. do the build i did in the video

2. power on the last lever

3. power off the last lever

aand you got the bug.