My understanding is that it's normal and they're all designed to release pressure in the event that it's over-pressurized. The easy fix is to take a little out of your reserve tank so when the radiator over-pressurizes, and throws fluid back into the reserve tank, it's got more room to throw more fluid.
Hope this helps.
"In the road of life there are Bimmers and there are Bimmers"
Mods: Full JDM lighting, APC bulbs, ///M rims, Four wheel Brembo rotors, Bilstein Touring suspension.