I have found that when I build the planed arrival using waypoints on the legs page that all goes well until you need to turn inside one of the waypoints, (normally a waypoint on the final approach which may have been at around 5 or 6 miles.) What I am trying to establish is why sometime the FMC will bypass the waypoint that the aircraft has turned inside of and other times the FMC will still look at the waypoint you have bypassed even through is is back behind the aircraft, and continue to calculate a VNAV path based on going back to the waypoint behind the aircraft and then to the next waypoint.
Cheers Mangatete.