Put the summary of the bug you're having here

What I expected to happen was...:
I thought I would be able to place end crystal on the obsidian

What actually happened was...:
the light block on top of the obsidian blocked placement of the end crystal

Steps to Reproduce:
1. place obsidian

2. place a light block on top of the obsidian
3. attempt to place a crystal on the obsidian, it does not work.

I expected it to work because you can place other entities and things where light blocks are no problem but not with end crystals.  this effects me because I wanted to use light blocks for my pvp arena but I cannot as crystals do not work now.