Unreliable NA matching in test instance

When inserting a question into the kth.test.instructure.com instance I find that the questions whose answr is the string "NA" do not work reliable, but the same question exported into the production instance works. See the figures below.

https://kth.instructure.com/courses/2139/quizzes/2902?preview=1

NA-not-working-20170712.png

https://kth.instructure.com/courses/2139/quizzes/2902?preview=1

NA-not-working-20170712b.png

The view from the live API of the last couple items:

NA-not-working-20170712a.png

If Instructure wants the QTI file - I can provide it, but otherwise I cannot post it here as the question is not mine.