Guild Wars 2

Hi,

Does anyone else is having situation like this:
Battle rage on, two zergs clash and more and more people are downed. Execution time!
I rush to kill whoever I can but in most cases I get nothing.
I manage to land minimum two hits, often more. Rarely I get exp.
Are there rules that I have to deal minimal damage or hits to be taken into account when enemy is killed? Sometimes I attack from afar but escape and in a minut or two I get exp and loot bag.

I’m necro MM with staff and axe+horn.
Maybe it’s a bug?

From what I understand, you have to do a certain percentage of damage to get any credit.