Can't delete all inventory items.

Basically I was testing out all of the new trapdoors, buttons, pressure plates etc. and I wanted to delete all my items in my inventory so, I pressed SHIFT, S and clicked the red X in the inventory and... nothing happened. If this was to be removed it would be extremely annoying to have to manually remove my full inventory. I don't know if this was intentional and it probably wasn't but please try and fix it thanks!