Ender Crystals introduced into the game in the over world via McEdit copy/pasting Ender Crystals out of schematics from the end and using the /summon command create the Ender Crystal in game as expected make the Ender Crystal, however after 1-2 minutes this Crystal becomes invisible and the player can no longer see the Crystal, the player can even interact with the block the Crystal is placed on to, which the player shouldn't be able to interact with because clicking that block should explode the Crystal as it has a larger hit box.
On re logging the player can see the Ender Crystals normally again, though they disappear once more after 1-2 mins, seemingly all at the same time.
Steps to Reproduce:
1. Add an ender crystal to the game via /summon or McEdit
2. Watch it till it disappears from your screen
4. Repeat steps 2 and 3