It can be reproduced with any pipe.
It happens on all sides.
First place a pipe (Hitbox normal): http://puu.sh/3WU0g.png
Second place a pipe next to it (Hitbox updates): http://puu.sh/3WU1F.png
Third break the pipe next to it (Hitbox doesn't update): http://puu.sh/3WU2J.png
Buildcraft 4.0.0

Yes, I noticed this in 1.5, not sure why it happens.

I don't understand why you removed all the packet stuff. How client is now sync ?

That packet stuff was dead code and wasn't being used