It turns out that the questions and quiz were not migrated from a Moodle 1.9 course. They were built in Moodle 2.4. So I think we can remove the "migrated quiz" issue from the list of reasons why this problem happened.
We've been looking at the database. Below, I've included the two entries for a random attempt for the question we're having a problem with. This is the only question in the quiz where the final entry includes "gaveup" as the state. I'm not sure if what I've included below is relevant or helpful. Does this tell us anything? Is there other data that would be more helpful?
| 44430 | 1801 | 11178 | 1 | 54.00000 | deferredfeedback | 65 | deferredfeedback | 143908 | 1.0000000 | 0.0000000 | 0 | 0 | todo | NULL | 2013-09-20 09:17:41 | 44430 | _order | 550924,550922,550926,550925,550923 | 58. The MOST accurate description of the way in which pyridostigmine prevents severe effects of an organophosphate is by:: Inducing the P450 enzymes that metabolize organophosphates; Binding to the organophosphate and inactivating it; Serving as a competitive pharmacologic antagonist of muscarinic cholinergic receptors; Preventing the organophosphate from forming a long-lived covalent bond with cholinesterase enzyme; Increasing the amount of acetylcholine available to compete with organophosphate for binding to the nicotinic cholinergic receptors | Preventing the organophosphate from forming a long-lived covalent bond with cholinesterase enzyme | NULL |
| 44430 | 1801 | 11178 | 1 | 54.00000 | deferredfeedback | 65 | deferredfeedback | 143908 | 1.0000000 | 0.0000000 | 0 | 1 | gaveup | NULL | 2013-09-20 11:34:18 | 44430 | -finish | 1 | 58. The MOST accurate description of the way in which pyridostigmine prevents severe effects of an organophosphate is by:: Inducing the P450 enzymes that metabolize organophosphates; Binding to the organophosphate and inactivating it; Serving as a competitive pharmacologic antagonist of muscarinic cholinergic receptors; Preventing the organophosphate from forming a long-lived covalent bond with cholinesterase enzyme; Increasing the amount of acetylcholine available to compete with organophosphate for binding to the nicotinic cholinergic receptors | Preventing the organophosphate from forming a long-lived covalent bond with cholinesterase enzyme | NULL |
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As I mentioned earlier, when I imported the quiz into a new course and then attempted the quiz (as a student), everything went fine. The answer to the problematic question was recorded. Also, when I previewed the quiz in the original course, the answer to this question was reported back.
And in case if it's any help, I've attached the XML of the problematic question. It looks OK to me.
Thanks again for any help. -- Brian