Put the summary of the bug you're having here

What I expected to happen was...:
to possibly place an Ender crystal on the bottom of an obsidian block

What actually happened was...:
I placed a block on top of the obsidian block, and was able to constantly place Ender Crystals on the same block

Steps to Reproduce:
1. right click an obsidian/bedrock block from the bottom (or sides) with an Ender Crystal.
2. repeat.
3. ...