Note1: this is confirmed only for 126.96.36.199; we don't have 188.8.131.52 on Xbox yet; or at least I don't
Problem: when building, for example, a bridge across a chasm, you should be able to crouch and walk backward with the Place Block button held down, placing blocks under your feet as you cross the chasm. Instead, it will occasionally place a block on top of the block you're standing on, pushing you off the bridge to die. Ask me how I know.
Steps to reproduce:
1. Put a stack of dirt in your hand
2. Find a ravine or chasm to cross, or simply start 1 or 2 blocks off the ground (for full effect, you want to be high enough to die when you land, or over a lava lake)
3. Choose a direction to build your "bridge" and face the opposite direction; for example if you want to build the bridge heading northward, face south
4. Crouch, walk backwards (facing south, but heading northward), and aim the cursor downward so that it crosses the vertical (north-facing) face of the block you're standing on before you reach the limit of your movement on that block
5. Press and hold the Place Block button while continuing to walk backwards
Expected Behavior: You can walk backward indefinitely, placing blocks as you go to build your bridge.
Actual Behavior: It will work for a few blocks perhaps, but eventually it will place a block on top of the very block you're standing on, pushing you off the bridge.