I should know how to fix this, I'm sure I've fixed it before.
I've got a portal surface on a south wall linked to a portal camera pointing north, and the view through the teleporter comes out upside down. I think this is because of the direction of the surface in relation to the camera (opposite), but I do not recall the method of correcting it.
Help mucho appreciated. I trawled the manuals and google and came up with squat
"Maybe you have some bird ideas. Maybe that’s the best you can do."
― Terry A. Davis
Spawnflag is set to 4 for a static camera. My understanding is:
1 = fast
2 = slow
4 = static
But it's not documented that I can see. Either way, 4 sucessfully makes the portal static. Turning it off doesn't alter the upside downiness
More fiddling reveals that whether I set the angle of the camera with a target_position or just with the ANGLE keyword, neither makes a difference
"Maybe you have some bird ideas. Maybe that’s the best you can do."
― Terry A. Davis
Try flipping the portal texture 180 degrees with the surface inspector. I doubt the image has any dependence on the portal shader, but because I don't know, it's worth a try.