Today, I flew this FP

[flightplan]
title=KJFK to EGLL
description=KJFK, EGLL
type = IFR
routetype = 3
cruising_altitude=0
departure_id=KJFK, N40* 38.39', W73* 46.74', +000013.00
destination_id=EGLL, N51* 28.65', W0* 27.68', +000080.00
departure_name=New_York_John_F_Kennedy_Intl
destination_name=Heathrow
waypoint.0=KJFK, A, N40* 38.39', W073* 46.74', +000000.00,
waypoint.1=BETTE, I, N40* 33.55', W073* 00.70', +000000.00, BETTE3
waypoint.2=ACK, V, N41* 16.91', W070* 01.60', +000000.00, BETTE3
waypoint.3=BETTE, I, N40* 33.55', W073* 00.70', +000000.00,
waypoint.4=ACK, V, N41* 16.91', W070* 01.60', +000000.00,
waypoint.5=KANNI, I, N42* 38.00', W067* 00.00', +000000.00,
waypoint.6=NANSO, I, N44* 29.33', W056* 04.27', +000000.00, N31E
waypoint.7=RAFIN, I, N44* 53.00', W051* 48.28', +000000.00, N31E
waypoint.8=VODOR, I, N44* 56.20', W051* 00.00', +000000.00,
waypoint.9=4500N 05000W, I, N45* 00.00', W050* 00.00', +000000.00,
waypoint.10=4600N 04000W, I, N46* 00.00', W040* 00.00', +000000.00,
waypoint.11=4800N 03000W, I, N48* 00.00', W030* 00.00', +000000.00,
waypoint.12=5000N 02000W, I, N50* 00.00', W020* 00.00', +000000.00,
waypoint.13=DINIM, I, N51* 00.00', W015* 00.00', +000000.00,
waypoint.14=ELSOX, I, N51* 00.00', W014* 00.00', +000000.00,
waypoint.15=EVRIN, I, N51* 46.93', W006* 33.80', +000000.00,
waypoint.16=NEKAP, I, N51* 43.58', W005* 17.43', +000000.00, UL607
waypoint.17=ABDUK, I, N51* 38.57', W003* 48.02', +000000.00, UL607
waypoint.18=NUMPO, I, N51* 36.60', W003* 17.02', +000000.00, UL607
waypoint.19=OKESI, I, N51* 26.60', W002* 03.70', +000000.00, UL607
waypoint.20=BEDEK, I, N51* 22.25', W001* 33.52', +000000.00, UL607
waypoint.21=EGLL, A, N51* 28.65', W000* 27.68', +000000.00,


As I got to about 1,500 miles, I hit dep/arr and  I selected BIG1E (if I recall) and 27L.  I also selected BIG as transition.  I fussed for quite some time as the route had all sorts of U-Turns that did not look right.  

As I got close enough to start down it, all of a sudden it stopped following the route and just kept going straight.  I double checked VNAV and a/p were connected, next waypoint was BIG/303, if I recall.  Of course, I was somehow heading 279 (a full turn).  I forgot to mention that I had stepped away west of the field, so maybe there was something that happened...  Before BIG/303, I tried deleting a waypoiint, and going to BIG/303, but it would not go anywhere, other than straight ahead.  I then disconnected ap and proceeded to do visual approach to finish the flight.