When I entered the end for the first time a bunch of weird stuff happened. The seed is: -8300275442758179407
I'm not sure it's all related, but the first thing was there were no end crystals. Just fire where they were supposed to be. I could put the fire out by left clicking, but it would just reappear. I could also put an item on the top of the block, but when I removed it the fire came back. Breaking the block made the fire disappear, but it would come back if the block was replaced. The block didn't have to be bedrock. Any block in the original spot would work. (see pic "end crystals")
There were no energy lines from the dragon to the end crystal areas, but he was still healing after taking damage.
If the dragon was flying and I backed up far enough he would freeze in mid-flight until I approached him again. And when I say he freezes, I mean he stops moving. His body is still doing the flying motion, it's just happening while he is hovering in the air.
I jumped off the edge and died, then re-entered the end. Everything seemed like it was back to normal. But previously I had replaced one of the bedrock pieces with sand, and this is what it looked like on my return. (see pic "end crystals 3")
Edit: Okay, the dragon still stops flying mid-air, but the crystals were back to normal.
It happened again in the same seed in version 18w20c. Except this time there was 1 end crystal and the rest of the blocks were as stated in the OP.
Edit: Dragon is doing the hanging out in one spot thing as well. Also there was no dying sound when I fell out of the world in the end. Not sure if this is related or not.
After dying and going back all the crystals have returned same as before.