Even when pine is kiln dried, there is no guarantee that the sap has crystallized or if it is still flowing. It takes years of air drying to totally dry up the sap. While it is still fluid, sap can work it's way though just about any paint.
It is shellac, or a shellac based primer that can block the sap. Shellac however is not a durable finish, so use it only as a primer which effectively blocks the movement of the sap resins, and then put a durable finish coat over the top.