Brief Description:

Trial Spawner's hitbox is smaller than a full block, but larger than 14px.

Steps to Reproduce:

1. Place a smooth stone, a trial spawner and a honey block from bottom to the top.
2. Press key "W" to move next to three blocks.
3. Press key "Space" two times while "W" is down.

What you see: 

1. The player can stand on the smooth stone.
2. The player can stand on the trial spawner.

Conclusion:

1. The hitbox width of a trial spawner is smaller than a smooth stone (16px). [Bug]
2. The hitbox width of a trial spawner is larger than a honey block (14px). [Works As Intended]

What it should be:

The hitbox of a trial spawner should be 16px.

Why this should be a bug:

When you replace trial spawner with a monster spawner, these phenomena don't exist. In other words, monster spawner is a full block.