Minecraft wiki entry for List_of_broken_features, associated text: As of 12w34a, the nether portal screen effects[2] and trigger sound[3] will play even if the player arrives on the other side of a portal, making the brokenness of this exit animation hard to spot. It is still noticeable given that this wrong animation starts weak and gets more intense as if this were a newly entered portal, rather than beginning at full intensity.