I created a wind tunnel as in figure A here:
https://drive.google.com/open?id=0B8v_WdcS3T18SUJ0TTNqTEg2VEU
The black lines are the geometry of the tunnel. The red box and blue box are two trigger_push volumes that push in the direction indicated by the arrows. The green line is the trajectory followed by the player.
I carefully calibrated the positioning and strength of the push volumes to give the player a perfect trajectory up the center of the vertical pipe.
All of a sudden, without me chaning the position or key values for the trigger_push volumes, the trajectory of the player in the tunnel changed to that in figure B (i.e. he collides with the roof of the tunnel before being blown upwards.
Does anyone have any idea why this might have happened?