Check your SID waypoints one by one because I noticed that FMC creates strange waypoint just after starting airport and if u turn on LNAV directly after TO your plane will turn to this waypoint. Maybe this is the problem only with my JS or specific airports but I almost always have to delete next waypoint after airport. Truth is that if ATC is operating you probably never turn your LNAV on just after TO but you'll get the command "heading" od "direct to". If you have similar problem with SID's in JS41 pls let me know because I don't know is it problem with my plane FMC or AIRAC installed. Sry 4 my poor english.