Hitbox bug with repeaters

Hello.
I found an "hitbox bug" :
I built an redstone system, they're two repeaters and bricks ( like this : http://i.imgur.com/r3e6ZJL.png ), when I walk on the repeater like this:
http://i.imgur.com/QJd1mz8.png ; I can go below, it works, but, when I want to walk on the repeater like this:
http://i.imgur.com/5IS3YfO.png
I'm blocked.

I think it's a bug...
Thanks.
Good bye.

Ps : Sorry for my english... I'm 12...
EDIT : Twisted decor is a shader