To make things clear right now : it's not a bug. The game is currently designed like this.
I just wonder why the Kobra and Holo aimpoints look so fuzzy & poorly detailed compared to the red dot and the OKP-7. Especially the holographic aimpoint, which makes aiming harder than with iron sights since the bleeding light covers way too large of an area to actually see your target. The Kobra suffers from the same bleeding effect yet in a way less dramatic extent.
Will it be fixed, or is it a feature ?...