Today I had 4 dragunovs in my backpack (note - all were in backpack, not 3 in backpack and 1 in hands). Since I am not too fond of dragunovs and nerby armory wanted 3 of them to be delivered, I decided to sell all of them AT ONCE. I did expected to be paid 4x4 RP for 4 dragunovs worth 4 RP each, and 3x100 RP as armory wanted to get 3 dragunovs and pays 100 additional RP for each, so that should be logically 316 RP. But I got 416 - armory decided to pay me additional 100 RP for 4th dragunov, even thou only 3 were requested. Now, in my case that is not big deal, as 100 RP does not make too much diffrence. But it does make room for exploiting - one technically can grab 10 requested weapons and sell them for +1000 RP (I am not sure how it would work with more than 4 requested weapons, but I do not see reason why it would not work the same as with 4).

Bug? Or feature?

Certainly a bug.