IIRC the slight over-pressurization has to do with change of airflow around the fuselage during rotation
That I don't know enough to comment, but with open valves the speed of the aircraft will reduce cabin pressure below the outside static, to be seen in unpressurised aircraft with the static source using cabin pressure as when static line behind instrument panel becomes disconnected. Acceleration will show a climb on the VSI (cabin pressure reducing) and de-acceleration a descent (pressure increasing). Had it occur on one occasion.