Can walk through 2×1 pathway with carpet on fence/fence gate if holding sneak pressed

[Wuzzy2]

If you build a structure like this:

BBB
B.B
B_B
BGB

B = Solid block
. = Air
_ = Carpet
G = Fence gate

You can't walk through if you walk normally because of the overhigh collisionbox of the fence gate. This is intended.
But you CAN walk through if you hold the sneak key pressed while moving to the gate. But this pushes your head inside the top block. Pretty funny/weird. This is because you are actually standing on the overhigh collisionbox. This should NOT happen.

Possibly related to engine, but maybe I can find a workaround.