Hello and welcome to JustAnswer!
Was this not happening with the last master cylinder? If this is a new problem since it was replaced then most likely you got a bad one.
When it acts up you can try loosening the master cylinder at the booster. If this allows them to unlock then you have a booster problem.
If they are still locked and it's all four wheels together then the master is most likely the problem. You can crack the lines at the master and see if they will release, if they do release but not when loosening the master cylinder from the booster then the problem is in the master.
no problem is new isw booster push rod supposed to be fixed in position as this one is very loose it enters the rear of the master cylinder but is not stable