Describe the bug
Sometimes some blocks becomes invisible when watching through Knowledge Gem above the enchanter.
You can see the faces of blocks adjust to it, even though the faces should not be rendered.
Known blocks can be invisble: gem lamps.

To Reproduce

1. Build a enchanter structure. Do not insert the Knowledge Gem now.
2. Place a gem lamp at somewhere, it is recommended to place at least 8 blocks away from enchanter.
3. Insert the Knowledge Gem.
4. Watch the gem lamp through the floating knowledge gem above the enchanter.
5. You may see the gem lamp disappeared.

Expected behavior
The gem lamp should be always there, regardless of how I watch it.

Mod version
1.7.0-deeper_down-alpha-21

Screenshots

Crash Report
No crash.

The bug cannot be always reproduced. The longer the Knowledge Gem is inserted, the fewer the chance to reproduce is.