Here is the reply that I got on Flight Simmers AFCAD Discussions forum..

"It's inherent in the way Flight Simulator works. Not a lot can be done about it without detailed tweaking of each airport.

Basically you have to try and have a node just a little down the runway from where planes reach taxi speed. Then hopefully there is a taxiway exit further down the runway which is closer than the one behind.

FS AI aircraft will turn go to the closest node when they reach taxi speed. If it is behind them they make a u-turn. The aircraft turns based on the radius set in the model file - which usually means turning into the grass.

On some airports you can fix this with a lot of work. On some airports it cannot be fixed because normal procedure is to back taxi."

Ok here we go do this,at some airports they do not have taxi way. This is because #1 no room to put in a taxi way or #2 DOD no money going into the airport to put them in, cost to much money or not enough traffic to mess with. So, what you can do is build your on taxi way try this and this will work.
dy