Next back buttons not working as expected after a quiz

Hi 

I have some content slides, followed by an instruction slide for a 3 question quiz and then a completion slide for the quiz. I have set the quiz to unlimited attempts so that the user will eventually progress to the completion slide.

However, when the user completes the quiz and on clicking back button on completion slide, the user is taken to the instruction slide (instead of the last quiz question...this is still ok) and on clicking back here, the user is taken forward to the completion of the quiz slide instead of the content slide that precedes the instruction slide of the quiz.

The above scenario only happens after having completed the 3 question quiz.

FB