Hoppers with barrel facing downwards on top picking up items. If you use a sticky piston to push a block into a shulker box to break it, it sometimes ends up in the close by hopper that has barrel on top.

Steps to reproduce:

1. Place down a shulker box. Color doesn't seem to make a difference.
2. Place 3 hoppers point to the shulker (all 3 hoppers are on the same y level with the shulker box), and place barrels facing downwards on top of all hoppers. Note that if there is only 1 hopper with barrel on top, the problem doesn't seem to appear; if barrels face up, the problem doesn't appear either.
3. Place a solid block next to the shulker box. Now the shulker box should be surrounded by 3 hoppers and a solid block. (There should be some picture attachments if I did upload them correctly)
4. Push the solid block into the shulker box with a sticky piston to break it. Place down another shulker and repeat this process several times, since it only happens occasionally.
5. After that check the hoppers. You should be able to see shulker box(es) in one or some of the hoppers.