cryptopia is a scam site, they are using bulwark coins to make master nodes to take rewards and dump them....
That doesn't make sense. No really. I'm not defending cryptopia, but they don't have enough resources as it is to run the exchange, they couldn't possible be keeping bulwark coins to run masternodes on their own servers.
What you are most likely seeing are people buying BWK, withdrawing them, then setting up masternodes. But not the exchange itself.