As far as I can remember BE 2012 only shows you one set of selections in the restore selection tree and then after you select the data and move on through the restore dialogs, if it detects the same data on two different storage devices (as duplicates) and gives you a choice of where to restore from. Note: 2010 R3 and eaelier used to show 2 sets of selections in the restore selection tree
So I guess the question is where are you expecting to see the duplicate set listed (maybe a screenshot would help
If you can see it working from one duplicate job and not for another however then you will probably need to log a formal support case for us to review what is going on.