I'm having trouble working out exactly what is going on here, but in my course, I have 15 sections each with about 3 items and can not move them about without causing mayhem.

If I move 11 onto 7 it makes them swap, instead of inserting 11 in between 7 and 6. Next time I do the same with the new 11 and 7, it works OK. Arranging all of them into a different order (5 operations, firebug shows no AJAX problems), then refreshing the page leaves me with a mess.

I've made a test course to illustrate (attached) which has the topic labels numbered so that initially, section 1 is labelled 1, 2 is labelled 2 etc. This lets you know the original order.

To see the mess, arrange the topics so that they go 1 3 5 7 9 2 4 6 8 10 by dragging 1,2,5,7 & 9 up onto 2 one by one. Then refresh. I ended up with 1 3 5 7 9 6 4 8 2 10.