The Bug:

Headless pistons render their piston head. This is not consistent with Java, where headless pistons do not render their head. This bug also works with sticky pistons.

Steps to Reproduce:

Obtaining the Headless Piston:

1. Place a piston and power it.
2. Use Ctrl + Pick Block to get the headless piston while aiming at the piston body. That Piston should have (+DATA) in their lore.

Placing the Headless Piston:

This is where the effects of the bug actually begin.

1. Place down a redstone block somewhere.
2. Using the piston you just obtained from Ctrl + Pick Block, place that piston on the redstone block. 
3. If for any reason the piston quickly retracts and extends back, break that piston and repeat step 2 of Placing the Headless Piston.
4. Now look at the glitched piston you just placed down. The piston body has a single block of an outline box, and its piston head renders without the visual piston head having a hitbox or a collision box.

Attached Minecraft World:

This is another way to reproduce this bug for those not on Windows or for those without a keyboard.

1. Download this attached world: Headless Pistons World.mcworld
2. In this world, there will be 3 normal pistons and 3 sticky pistons. The normal piston and the sticky piston to your left are a set of pistons that physically contain both their head and their body. The set of pistons in the middle are normal and sticky pistons that are both headless, with a fence replacing the piston head, even though their heads render. The set of pistons to your right have a normal and sticky piston that are both physically headless, even though their heads visually render. There is also a chest which contains both types of headless pistons that can be used to reproduce this bug. The pistons in the chest will have (+DATA) in their lore. Signs are used to tell which type of piston it is, whether headless or not.
3. The set of pistons in the middle and the right render their head, even though they are really headless. This should not happen.

Expected Results:

Headless pistons will not render their head. Please note that headless pistons can only be obtained legitimately by following the steps to obtain the headless piston.

Observed Results:

Headless pistons render their piston head. This is not consistent with what happens on Java Edition.