Left hand placing block not held

In creative mode: I was in my inventory clicking my armor slots with a blue stained glass block, put it in my left hand slot, and then removed it by putting it in the destroy item slot.

I then was able to place the glass block by right-clicking even though nothing was in my left or right hands. Placing the block made no sound or animation. The block was still breakable and made noise when broken after being placed, however.

Couldn't replicate it after using pick block with scroll wheel.