As a warning, when doing SCJP, if you try to review the drag and drop questions you have already answered, your answers can disappear meaning you have to do the question again. Speaking with some colleagues here who just took this exam, the problem seems to affect this exam as well.
Yes - it's a known bug (or should I say "feature") in the
testing engine. Your test centre should give you something to write with though - paper/pen or a small whiteboard/marker etc. My advice is that for each DnD question you answer, just jot down a brief outline of your answer on hardcopy. That way, if you do want to revise it later, you'll still know the order you used before in the event of panic onset, and won't lose it altogether!
Charles Lyons (SCJP 1.4, April 2003; SCJP 5, Dec 2006; SCWCD 1.4b, April 2004)
Author of OCEJWCD Study Companion for Oracle Exam 1Z0-899 (ISBN 0955160340 / Amazon Amazon UK )