Jesse does this too and cant roll back (drives me bonkers during the day time when he's on his mat!), but once he's been on his tummy for long enough or if he does it during the night he'll yell out. I thought being in a grobag sleeping bag may prevent him from rolling but he does it just as easily in it anyways. So yeh.. think we just have to wait until they learn to roll back... though i have been told about triangle sleeping pillows (for babies) that will stop them from rolling.. but Jesse is that strong i think he'd find a way.