1. open VIRTUAL ARSENAL
2. use ASP-1 Kir 12.7 mm with the sight of "Nightstalker"
3. use full optical mode (right-button of mouse by default)
4. activate the thermal or night vision on your sight (N-button by default)
5. try to switch aiming between the upper and lower sight (left Ctrl + right mouse button by default)
6. will get the result: After returning to full aim optic, or thermal/night vision sight disappears and always required re-activation.