Hey mate,
i?ve been flying the RPMs since 2010. Never had this problem. But i also work for a kiteschool and there we had lots of Slingshot Z, where this happened. Doens?t matter which year it was...2012...2013...same Problem. And i do have lots of friend, who are riding the RPM too. Never headr about this problem.

What did the shop said about your problem? Which kitesize it it?