Emrakul, the Promised End didn't let my opponent take their extra turn. I cast Emmy, took control of my opponent's turn, and then when it was supposed to be their turn it became my turn again.
Battle log with opponent as xxxx:
17:11: Turn 24 thenumber23 (4 - 27) //turn when I cast Emrakul
[...]
17:12: Ability triggers:
Emrakul, the Promised End [364] - When you cast
Emrakul, the Promised End [364], you gain control of target opponent during that player's next turn. After that turn, that player takes an extra turn. - targeting xxxx
[...]
17:13: xxxx takes an extra turn
17:13: Turn 25 xxxx (4 - 27) //during this turn I was allowed to control my opponent
[...]
17:16: Ability triggers: At end of turn xxxx lost control over xxxx.
17:16: Turn 26 thenumber23 (4 - 27) //then it became my turn again, without xxxx getting to untap or draw
I don't know if it's relevant to the bug, but we had a rollback during the turn I controlled my opponent, to the start of the the current turn.