Usually the rubber seal around the top of the dipstick gets old, plasticized, and shrinks and can no longer keep a good "grip" on the dipstick tube... when you crank the boost up, the pressure can leak thru the valve stem guides or piston ring blowby and of course, pressurizes the crank case. soemtimes, it can be more pressure than the PCV can vent out... but the vent tube in the cover by the CAS is also able to release the pressure, so the condition of the PCV wnot be the only thing that causes the dipstick poppery.

I made an actual lock that clamped the top of the dipstick, and then had the end of a hose clamp that hangs down. then the other half of the lock was clamped to the tube itself and had the other end of the hose clamp sticking up. you insert the dipstick till the 2 hose clamp ends meet, then tighten the screw like a radiator hose, and it would draw the dipstick down and lock it in. works like a charm... just tedious. ill have to see if the crimping will hold under 20psi, as soon as im tuned and have some xylene