[ART] Reflective rectangle outside the cockpit

In the Viggen cockpit model, there's a rectangle outside the cockpit - left of the SPAK light - that glints in the sunlight:

I can try to capture some video of it later if needed, but as you can see in the image, it's not a soft reflection that continues to rotate around the canopy as the angle to the sun changes. It has hard edges where the reflection suddenly stops.

Edit: This seems to have come up in a previous thread as well: https://forums.eagle.ru/showpost.php?p=3775309&postcount=7