Your setting the door passable, is the gravity trace using IGNORE_PASSABLE flag? You actually should not set the door passable. What might be happening is a timing error. You set the door passable, then walk in to it, the reset passable - making it solid. That will cause the player bbox to be in the door as well as the gravity trace to be in the door. Gravity trace hitting inside a door will cause a negative trace return, which would cause the player to fly upward.
This looks like the most likely issue. The flying off is done once the player enters the door. Once the door is open, should it be set as passable then?
