At least, Mark, reading from your experience was fun.  :D

I'd really like to help you there, but I don't have a clue where to start. That turning away motion could arise when you were too late on changing the ADEU cards.
Civa then reads the next waypoint (which is one that's already been used) and tries to turn to it, so the backward direction will become active, I think.

Before this happens (running out of current waypoints), those ALERT signs will start to blink (not only light up, as they do when getting close to a new waypoint) though.
I've had this on stages where you should change the ADEU card when going from 6 to 7 on the list and the distance there was like 2nm or so.
Or I forgot to watch my Civa and only wondered why the plane takes such a strange direction. Luckily, when you realize this thing happening, the HDG mode can be used, the Civas get a new ADEU card and you then can look up the next waypoint on the Civa's list.
In the meantime, you can correct the heading roughly via the bug or, when you were to late on realizing, fly a circle and continue like nothing has happened.
Maybe say something like "oh, dear passengers, did you see that small house on the left side? So cute!".

Always have that small text file open which is compiled by the flight plan converter. It shows you all distances (so you can prepare for such short ADEU interchange times) and also lets you plan ahead.