PP - congratulations and good luck. I really do think that the "be wary of it" line is the best you could offer. The only other 'simple' explanation I can offer is that there may have been some 'above/belows' in the original which then become irrelevant? Otherwise it is just unreliable black magic.
If you get your trainees to keep their own mental plot on the profile you will have been very successful!
Edited to add: In my experience, NG and Classic, it doesn't even take a 'Direct to' to make it screw up the descent
. Even with correctly programmed winds etc it never quite takes the prize. In any case, let's face it, how often is your descent 'as planned' anyway? 3x +/- wins all.
If you want a laugh, ask your 'training' trainers to explain it.......................