Note: this is all on copies of the same Survival world. I never entered Creative mode. I also had hardly any lag, it seemed to be running smoothly.

When I enter the End everything seems normal. I start to fight the Ender Dragon by shooting the Ender crystals.                                                   

1.Whenever the Ender Dragon exits my render distance the boss bar disappears (I don't think this is a bug) which seems normal, but then, occasionally, it despawns entirely, dropping nothing (and not spawning the Ender Dragon egg)

2. From the beginning (or should I say End ) the bedrock portal back to the overworld is already ignited, active (I've tested it), and sometimes it has the torches on it, sometimes it doesn't.

3. Once I had destroyed the Ender Crystals and tried to fight the Ender Dragon I could only damage it with arrows (and, of course, only when it was flying), when I tried to hit it with a sword while it was on its bedrock pedestal I got the Critical Hit particle effects (I was jumping up and down to get the hits) but the Ender Dragon didn't flash red, make its "Hurt" sound effect, or take damage on its boss bar.

4. When I killed the Ender Dragon (in Survival) it only dropped enough xp to bring me to 20 levels (I started with less than 10 levels, but more than 5) which seems to me to be much less xp than normal. It also didn't spawn an Ender Dragon egg, or a portal to the End Islands.

5. Neither the Ender Dragon egg nor the End Island Gateway spawned the whole time I was testing this.

6. When I died or hit "Save and Quit" and then reentered the End or game (depending on which thing I did initially) the Ender Dragon would be gone (presumably despawned).

7. When the Ender Dragon was either dead or despawned I would periodically hear a very glitched out noise that sounded sort of like an echo-y vibrating grinding sound (it was very clearly not the Ender Dragon death sound [at least not without being very distorted], or a part of the music). It sometimes played during music, but mostly just when there wasn't any music

8. Endermen didn't drop any Ender Pearls. I killed many Enderman with a looting III sword and didn't get any Ender pearls. I then looked around to see if the Endermen had somehow teleported them away, but it didn't seem as though they had.

9. I get no Achievements related to the Ender Dragon aside from "enter an end portal" I also don't get the "You need a mint" achievment, even though I picked up both breath from the fireball sorta thing the dragon fires at you, as well as from what it breathes out around the pedestal when you get to close.

Note: later, in Creative mode I flew out to the End Islands and the End Islands, End Cities, and End Ships all seemed to be normal.