A Month ago a took a hand held gps with me onboard AMS-SFB / MIA-AMS. The outcome of the route did raise some questions like yours too. Like why heading to the US from Europe we flew way more north than the great circle and back to AMS from MIA we almost flew straght to AMS.
Have a look at this:
Same thing here. performance is getting better and better with some tweaking around, I get a steady 35 fps in the VC at takeoff. but fps plunges when the mouse cursor shows up to around 17~19 fps... I hope this is able to fix with a patch or something I wont get far without a mouse :-) Ruben Hofs