Offline test is not submitting all answers

Test made available offline randomly don't submit answers to the moodle server.
In the question overview before committing the hole test, these questions are marked as not answered even though if you click on them they are!

[Edit]

We are using a custom question type of "multichoiceset" but i'm sure this is not the source of this issue, since it works fine on not offline tests and the not submitted questions occur randomly from iPad to iPad participating on the same test.