Limiting 'Questions per page' causes previously correctly answered questions not to be included in the final score

Setting a quiz in which the number of 'Questions per page' is limited causes previously correctly answered questions NOT to be included in the final score.

So, for example, there are 10 questions in a quiz.
'Each attempt builds on the last' is set to 'Yes'
The number 'Questions per page' is limited to 2.
In the first attempt a student answers the first 6 questions on the first 3 pages correctly, and so gets 6 out of 10.
In the second attempt, her first attempt choices are displayed, so there is no need for her to answer these questions again.
The student goes to the last 2 pages that she did not answer - the 4 remaining questions.
She chooses the 4 correct answers.
She SHOULD then get 10 out of 10.
However, as things stand at the moment, she only gets 4 out of 10.

I have experienced this bug both on my own moodle system, and have reproduced the problem in the http://demo.moodle.org/ site.

This bug can be reproduced regardless of the scoring method or other settings. The common denominator appears to be if the 'Questions per page' limit is set to anything less than 'unlimited', and 'Each attempt builds on the last' is set to 'Yes'.

The attached screen shot is from a student's point of view. The first question was answered correctly in the first attempt, but after having the second attempt scored, it appears to have been ignored. There is no indication about whether or not the question is correct. The second question with the green feedback was not answered at all in the first attempt, but was answered correctly in the second attempt.

In the teacher's view of the second attempt, the feedback under each question appears as expected, but the reported total score is only the score for the questions answered in the second attempt that were not answered in the first.