When a pipe is moved by a piston, it does not properly update any networks it might have been, or now be, attached to. This means machines can send essentia to each other even if they are not actually connected with pipes, or machines that should be able to send essentia to each other won't.

One fix could be to blacklist pipes from being moved by pistons, but I think pistons + pipes would be too useful of a control mechanism to be removed.

Fixed in 1.0-rc1.