While standing on a wood slab in my friends base on a snapshot server, I was using the crafting table and then exited to check a crafting recipe. Doing that resulted in the items dissapearing, and one of the items taking the place of your Boots, deleting the boots.
I confirmed this by testing with multiple items, but it cost me Feather falling IV boots
Edit: After more testing, it affects all crafting tables, wherever you are standing on a half slab or not
Edit: scrap that, I just went farming and the sugarcane also appeared in my boot slot. Same with dirt I mined. Also picks up extra blocks but does not give them to you. eg: farming 20 sugarcane, but only getting 1