20w20b- cant do anything with the block in the top right of inventory

I was trying to make a quick hoe and found that the anything the top right slot would be treated like it wasn't there. I tried this with wood, cobble, and iron at a crafting table, furnace, and just my inventory. It only seemed to recognize something was there if i was using a chest.

I wanted to grab the cobble in the top right of my inventory

I was unable to.

I do not know if its able to be triggered or not, but here's what i did.

1. Use crafting table, furnace, or open inventory with E. (the inventory slot works fine when using a chest)
2. try to grab block in the top right spot.
3. it wont.

my temporary solution-

1. open a chest
2. replace the block in that slot(top right) with something you aren't using to keep something you want to use from going there.
3. Go about your day.