[Expecttheunexpected]

I don't know if I can blame any broker for refusing to accept the trades of someone who gets in and out too quickly for them to cover properly. A broker is in business to make money, not to provide a public service. If one of their customers is costing them alot of money they have every right to refuse his custom in future, just as a pub can bar entry to anyone they feel like banning.
Refusing to pay out on trades is something else entirely of course, but I've never heard of Oanda doing that. Overall they sound pretty honourable, especially by most brokers standards!
(...this probably sounds like it's coming from one of their staff but I've only ever used their demo account; I'm just another several-hundred-pounds-down SB punter using IG and Cityindex)