Medusa - KS Bug?

So We are all in swamp event, and i spoted 2 medusas, killing them at the same time.... was killing for 90seconds(it takes me 1-2minutes to kill one) then Sunny the FR came and did one hit(or couple) boxes droped, and i was not able to pick them up... he took the boxes and wen't away. not sure if this a bug or what? why didnt i get the right to pick up boxes since i did most of DMG?

 

It's all about who deals the last hit.

 

Is that fair?

 

Fair or not, that's how webzen made the PvM system