Why does the cap unscrews will blending causing the liquid to leak out

I have same problem. I purchased new gaskets & new containers. The new gasket worked for a few months but problem has returned.

It’s resistance on the blades that is unscrewing the cap! If you’re mixing soft fruit and liquid only, this wont happen. An overloaded cup and/or hard items such as carrots Ice and the like is also problematic. cut the these things fine or crush them before placing in the cup and add water. Another thing to watch is those little lugs on the cap that insert into the slots that start the motor, push down only to pulse..if it pulls to the lock position on its own trouble usually ensues! Anyway this has been my experience, I hope this is of some assistance.