Not only the property but the denomination controls the retirement accounts for the pastors. If they leave they can also lose their retirement.
This statement is not true. Participants in the PCUSA Board of Pensions are fully vested after three years. That means that most pastors vest during seminary. The Board of Pensions is actually one of the bodies related to the PCUSA that is not monkeying around - at least on the Pension side of things. See: http://www.layman.org/wp-content/uploads/2013/02/pension-brochure.pdf