Can't enter other answers after an incorrect answer

I have implemented an articulate presentation in one of my courses and have had MANY emails from my students complaining that when they enter an incorrect answer into a quiz and then are unable to try to enter a new answer.  I have been telling them to exit and then re-open the program and when it asks if they want to start off where they left say 'no'.  This has worked fine, but I would like to figure out how to get rid of the issue completely.  Is it possibly a setting I have switched?  A browser issue (I use Firefox and cannot recreate the issue they are having)?  A bug?