Ok, I see, the confirm page has the data set to store on post from the checkout page.
Double click the store order summary behavior, select the column that is storing the list values and edit the code for that column from:
<?php echo isset($_POST['InterestedIn'])?$_POST['InterestedIn']:""; ?>
to:
<?php echo isset($_POST['InterestedIn'])?implode(", ",$_POST['InterestedIn']):""; ?>