Weapon attachments/skin bugs

I cant seem to attach any unlocked attchments on the M45A1 Pistol (Muller skin). it says ive unlocked some, on weapon lvl 4 but they cant be attached.

Another thing, the weapon blueprints doesent save your chosen attachments. I dont know if that is a feature or a bug too. Like if I chose the M433 "shouded" skin/blueprint it comes with pre attached attachments, but if I chose something else on it it doesent save.