When holding any tool (pickaxe, axe, shovel, hoe, flint & steel) (except clock or compass), or any weapon (sword or bow), with a full hotbar, using pick block will not work on any block that is not in the hotbar.

Steps to reproduce:
1. Be in creative.
2. Have any item or block in each slot in hotbar.
3. Hold any of the above mentioned in hand.
4. Use pick block feature on any block that (what it gives you using pick block) is not in the hotbar.

Note: In superflat world with 'Redstone Ready' Preset modified to not include stone on bottom