Re: Data of Opaque attempts disappear.

I can't really remember how this worked in Moodle 1.9. That is ancient history as far as I am concerned.

I don't think the teacher comment is significant. Can you try this alternative test:

1. Create a quiz containing two questions on two separate pages. Q1 Opaque, Q2 true/false, on two separate pages.
2. Attempt the quiz as a student, answer Q1, then go to the next page, but do not submit the quiz.
3. Log out of Moodle and close your web browser completely.
4. Go back into Moodle, log in again, and resume the quiz.

Now can you see the responses to the question?

That is, I am guessing that your question engine does not get this bit right: http://docs.moodle.org/dev/Open_protocol_for_accessing_question_engines#Question_sessions_and_the_reproducibility_guarantee (but that is only a guess.)