Interactive Book loses results when navigated away from

hi All. Not sure how this is meant to work but seems a bit absurd. We have created loads of interactive books and were under the impression students could work through the books and it would keep their work and they could continue from where they left off. Kind of like normal tracking on a scorm or moodle lesson where it remembers your interactions. 

However we have found if you navigate away from the interactive book all interactions are lost. We have large books and students should not be expected to read the lot at once! We also tried submitting, hoping that it would save what we had done so far and when you comeback its all gone again. Surely this is not how it was designed?

We expect that you can go into the learning object as many times as you like until you complete it and then click submit to finalise the learning object. Is this a bug or a really big oversite?