It is far from ready yet but I think I found a potential vulnerability in DarkCoin which allows miners (actually pools) to not pay part of the block reward to masternodes.
DarkCoin wallet checks the following things for each new block:  
1) There is a payment to master node.
2) There is a payment with the same amount as a payment to master node should be (30%).
But there is no check that this is the same payment. This means that if you generate a block you can pay 0.0000001 DRK to masternode and pay 30% and (70% - 0.0000001 DRK) to yourself as separate coinbase outputs. Such blocks should be accepted by DarkCoin network just fine but I haven't tested it on testnet to be 100% sure.

Mr. Spread, have you found the part of the Darkcoin code where, "Enforcement" is on or off?  I THINK that may be what you're seeing as when enforcement is off, yes, that can and has happened.