Trying to remove an entry in pst MessageStoreProperties

Hello. I am trying to remove the property MapiPropertyTag.PR_PST_PASSWORD from a message store:

            if(pst.MessageStoreProperties.Contains(MapiPropertyTag.PR_PST_PASSWORD))

            {

                long passwordHash = pst.MessageStoreProperties[MapiPropertyTag.PR_PST_PASSWORD].GetLong();

                pst.MessageStoreProperties.Remove(MapiPropertyTag.PR_PST_PASSWORD);

            }

If I check for the existence of the property afterward, it does not exist, but if I close the store and open it again the property is still there.