I am using 1.4.3+ and have noticed a problem with quizzes which have opening and closing dates and times. Although I have set the quizzes for the exact times, they were open before and after the set times. The only thing keeping someone out of the quizzes right now is a password.
I have used moodle 1.2, 1.3, and 1.4 for quizzes before but never had this problem.
Not sure if this is the fix for everyone's problem, but I found a note that indicated that in versions 1.4+, the teacher of a course can take the quiz at any time, which turns out it exactly what our teachers were seeing. When they had a student try the quiz, they could not take the quiz. I think this probably applies to admin level accounts as well.
Hope it helps...
I'm sorry for the very late reply, but I've just been back recently. Yes, that clears it all up for me. Thank you very much! A big sigh of relief from me!