youtu.be/3m7fKOYni3o
Apparently, if you try to get items out of storage drawers that are directly above the floor but you have a full inventory, they pop out and seem to bug one block through it (on 2x2 and 1x1, I haven't tested others). So if the floor is 2 blocks thick, they get back to the top. But if there is e.g. void below as shown in the clip, they fall through the floor. Only happens when the drawer is one layer above the floor.

This is possibly fixed in 3.7.8/4.2.8. I raised the spawn height a bit, so hopefully that is enough to prevent any clipping. I couldn't reproduce clipping with the original height in testing, however.