Tested on Samsung Galaxy S6 (SM-G920W8), Android 6.0.1 MCPE 0.15.90.7

Example Steps to Reproduce:

1. Open a new survival single player world with cheats enabled
2. /give @p cake 60 (any non-stackable, placeable item will work and any quantity greater than inventory size will do)
3. Observe your inventory is now full and there's a pile of cakes on the ground.
4. Stand on or near the pile of cakes so you'll pick one up when you have inventory space.
5. Place a cake on the ground and observe that your selected hotbar goes empty, you hear the player pick up a cake and your hand immediately has a new cake in it.
6. The bug is the hotbar being empty when you've clearly picked up a cake after the "pop" sound (and you have one in hand!)

As far as I can tell, this doesn't duplicate any items. The bug should occur any other way you can arrange to stand on a pile of the same nonstackable placeable item and start placing them.

Note: If you drop the cake instead of placing it, everything happens correctly. This is why the bug seems to only affect non-stackable placeable items.