I was wearing the "Combat Gas Mask" and had the weapon "SG5-K".

SG5-K attachements on it:

• "SG5-K Folding Buttstock"
• "SG5-K Rail Handguard"
• "ATOC-Scope"
• "Pistol Suppressor"
• full "30rd SG5-K Mag" (and one Bullet in weapon"

So when crouching and scoping and than moving left or right, textures of the "Combat Gas Mask" will prevent looking through the scope
and you will see green textures.