Sphere of Annihilation and X Counters exiles itself
I cast Sphere of Annihilation with 6 counters on it. I allowed a turn to pass and the sphere triggered on my next upkeep. the sphere exiled itself, but the other permanents it should exile with the sphere, did not get exiled. this bug cost me the match. both my opponent and myself were baffled by the failure of the sphere to trigger correctly.
My Sphere with X = 2 didn't exile Collector Ouphe but did exile my own Karn, the Great Creator.
Sphere of annihilation seems to only work intermittently.
Had this one happen to me with 3 counters.
The same happened to me I cast sphere of Annihilation with 2 counters when opponent had an ornithopter and Ingenious Smith out, and neither creature was exiled, nor the Gingerbrutes or Stonecoil Serpent in the graveyard.