Hello Kevin,
I discussed with my dealer and he told me that in the last period he faced with this problem several times. He recommended me to go with my quad in the service. To solve this problem they will install a kit witch have the role to decrease the pressure from the engine crank case, this will prevent to blow the oil in the air filter box. After I discovered this problem on my quad I cleaned the air filter and I drained the oil from the air filter box. It's not normal to happen like this when you ride your quad. The best way it's to contact your dealer and ask him to solve this problem.
Hope to help you my reply.
PS. Sorry for my English
Regards,