It's like the reverse of
MCPE-13798. (This is NOT a duplicate of that bug.) When picking up lava/water with an empty bucket in creative mode, you will be given a lava/water bucket in your inventory, which shouldn't happen. This is not happening on Win10 Edition 0.15.10, so I'm not sure if this is a Pocket-exclusive bug or new in the 0.16.0 beta versions. Tested this in an Android emulator, though I would assume that has nothing to do with this kind of bug.