My glass is showing a weird behaviour: at a steep angle it either shows the exterior with barrel distortion, or shows the interior like a mirror. When looking parallel at the glass, these issues are gone.
The problem exists also with a simple glass shader. What’s going on?
I would guess it has something to do with the geometry. Either the normals are flipped or you may want to give it some thickness in case it’s just a plane. If you can’t pinpoint the issue, just make another plane from scratch, give it some thickness and you should be fine.
You were right - my normals were flipped. Thanks!