Device: Samsung Galaxy S 3 Mini (Kit-Kat AT&T version)
(Also bug persists in previous versions down to 0.10.0; which is where the bug was first reported...by me.)

The following steps to recreate the bug is the simplest way. Type of mode or type of world does not matter, but to reproduce easily, follow these simple steps:

Step 1: Create a superflat world. Find an area in the world, and dig a 3x3 hole (Bigger or smaller, whatever you are OK with) until you breakthrough the last layer of bedrock.

Step 2: Replace the last block placing layer (Which ist Y:1) with gravity-affected block(s) like sand or gavel in its place. Then, place more around it by repeating this step if it doesn't satisfy you.

Step 2.1: Do note that if you place sand-like blocks at Y:2 or higher with no blocks below it (so that it falls), it does NOT suddenly stop and make a block at Y:1. It continues falling into the void. The bug is that sand should fall even when placed at Y:1.

Step 3: It should float!

Please look at screenshot below for more.