Tested on Samsung Galaxy S6 (SM-G920W8), Android 6.0.1 MCPE 0.15.90.7
Example Steps to Reproduce:
Open a new survival single player world with cheats enabled
/give @p cake 60 (any non-stackable, placeable item will work and any quantity greater than inventory size will do)
Observe your inventory is now full and there's a pile of cakes on the ground.
Stand on or near the pile of cakes so you'll pick one up when you have inventory space.
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.
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.
This is a bulk resolve of issues that haven't been updated to 0.16.0+ yet. Please comment below (To open the ticket) and update your affected versions. If you cannot reproduce the bug, please write in the comments so we can resolve it as "Cannot Reproduce". Thank You!