I’m marking this as a bug, but it might be “working as intended”.
If you have 3 boxes of expensive flowers on your handtruck, and you bump into the rounded shelf, it only takes 1 box, even though it can hold all 3 and then some. When you bump into a storage shelf, it takes everything, and I personally, I think it should be the same on the shelf.
This wasn’t an issue with gifts since one box was enough to fill the shelf.