When a banner is normally placed on the ground and then, while aiming at the hitbox, you try to place a banner, it will be placed in the ground (screenshot 1), and also it will be missing a support (screenshot 2). Screenshot 2 created using a barrier block.

Steps to recreate:
1. Place a banner on the ground.
2. Aim at the hitbox.
3. Place a banner.
4. It will be in the ground.