AsoJan Even if you remove the complete path payment feature, the arbitrage is still possible with a high speed trading set up (similar to what people do with stocks, forex, products, etc). The arbitrage is possible because of a spread of the price not the features in the blockchain itself.
I think (but I'm not sure) you can stop it if you set the coin issuer so everybody need your approval to hold the coin, but since the guy is doing the arbitrage with the path payment feature I'm not sure if that applies... The problem is that the account that issued your coin is locked so you won't be able to test it (and I don't know if that's what you want to do with your coin because people won't be able to adquire it easily)