I have the same wheels, no problems. Did you rotofix the cog first, or retorque the lockring after a couple of uphill sprints? Do this because you will tighten the cog completely as you ride, and *then* you should tighten the lockring again before trying to skid or whatever.
Also, the mechanic at my LBS installed everything when I bought the wheels. He really took his time to make sure he didn't cross-thread the lockring. If the lockring is crossthreaded, it's not going to hold correctly (obviously). Don't use a cheap lockring either -- it's not worth destroying your hubs over a couple bucks (assuming they're not already destroyed).
And install a brake -- at least until you get this problem ironed out. Please.