in a small window of minecraft, the crafting table search menu goes over the crafting grid, with hitboxes turned on (F3 + b) you can see the hitbox of that little version of you through the overlapping search menu.
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The reason @unknown could not reproduce this issue is very likely because their graphics settings were set to "Fabulous!". If set to any other option, hitboxes should be visible in the inventory. I can also confirm this issue.
Relates to [MC-270355] (read latest comment from @unknown, also confirming the fact that this is dependent on the graphics settings).
I can't reproduce, with hitboxes on I don't see it in the inventory