There seems to be a bug when performing page drag and drop -- pages are not dropped sometimes. To reproduce:
1) get a clean WP 3.3.1 installation with 6 pages: p1, p11, p12, p2, p21, p22. p1 is parent of p11 and p12 and p2 is parent of p21 and p22 (or just use existing pages on your site, will probably work too).
2) collapse p1 and p2 of them and RELOAD "Pages tree view". p1 and p2 should be collapsed after reload.
3) expand p2 and drag p22 to p1. p1 should auto-expand. drag p22 between p11 and p12 (should show a green tick mark) and release.
To make sure that bug reproduction is correct, do NOT touch anything else with the cursor while dragging except the p1 that's supposed to expand and space between p11 and p12. To do this move the cursor immediately to the right after clicking to drag, and move left to p1 and to space between the p1 and p2.
Hope this description is detailed enough, tested it on firefox and chromium.