E.g. walking from the overworld to the nether in 3rd person
When the player is already in the portal but the camera is still on the other side of the portal, it should still render the overworld where it is visible (not purely the nether with an empty frame).

Most code for this should already be in place, just need to properly calculate the position of the third person camera.

Should be fixed by f6cd259 (once 0.2 lands).