Susan:

Very odd. It's just math and once done (even if wrong) the answer a second time should be $0. It's almost like something is not getting updated in the AP database so that next time you do a revaluation the calculation is done all over again with the same result (create a GL entry for the revaluation but don't update AP). So far none of my clients have brought this to my attention, which means either blind luck or the problem is unique to you.

This looks like a problem that requires some hands on with the database. You may need to get your Adagio consultant involved.