One way to reproduce this is in Girna, go to building "House 2 (big inhabited) v1", as pictured in the screenshot girna.jpg. Open the front door as seen in the lower part of the image, and the glasses appear. This occurs (at least) in Alpha release candidate version 0.5.102980.

EDIT:

Seems to happen in many buildings in Agia Marina with similar layouts. Only one door triggers it. The same type that has non-collision railings..

some kind of fix might be necessary, especially if other birds in full game have similar configurations. I played through the helicopter showcase with TIR, and had to walk shots to target - with minigun that was OK, but ran out of rockets pretty quick :)