Finish to Finish Relationships -with different calendars

We have an interesting situation in which a successor activity (Activity "B") is assigned to its predecessor (Activity "A") with a finish to finish relationship; however the two activities have different calendars. Activity A is allowed to occur any day of the year while Activity B can't take place on weekends and holidays. In our situation Activity A is projected to complete on the Monday of a holiday weekend and Activity B is restricted from taking place on that weekend. How does P6 calculate the finish date of Activity B when the Finish date of its predecessors is on a