Even in Garry's Mod, reality is subjective

So here I am dicking around on a TF2 map in Garry's Mod...

As you can see, I've placed two balloons, one on either side of a gate. When I approach the gate, the gate opens...

I can even get far enough away from the gate that it goes back down.

So far so good. Now let's activate noclip and fly off the map, leaving the camera where it is...

Er... that's not right...

Isn't that interesting.  It keeps the interior set, I guess because the camera is there, but it ditches the exterior and just splats up the skybox.