I think Paul is correct, although "flapping" or "flogging" are perhaps not quite the right words to use. I can't think of a word ("flutter" comes to mind, but that is something else and the subject of a different discussion) - a "tendency to flap slightly when luffing up into the wind" would be correct regarding SJR jibs, which are open-ended on the aft end of the batten.
I regard the panels on a conventional junk sail as being closed at both ends of the batten and only the camber provides enough surplus canvas to "ripple" a little when luffing up. Same as the mains on a SJR. The SJR jibs, however, are open at the leech, because of the added cloth needed for "sheeting angle", thus more surplus cloth and the ability for a bit more than just "ripple" when in the eye of the wind. Not flapping as much as a bermudan or gaff sail - but a bit more than a conventional junk panel.
That's just another way of saying what Paul has said.
I never thought of it before because I have never luffed up into a severe gale with my SJR, but I can imagine in that situation the conventional junk sail might be more robust than the SJR sail if exposed to prolonged abuse.
In the normal situation it is not a big deal - the jibs are relatively small, and they can't flog in the way a bermudan or gaff sail can - the junk rig advantage still applies, perhaps a little less of the advantange in the SJR jibs.
Still, this is something David T never quite "put his finger on" but has hinted at in the past, when cautiously noting that no-one yet has ocean-cruised extensively with SJR. It could be a weakness of SJR as an ocean-going rig, not yet discovered. (Not saying it is - just saying we don't yet know).
I don't want to re-start controversy and I have not experienced the slightest problem with my SJR, and like it very much. But ... "horses for courses" could possibly apply. I have never discounted David's caution in the area of long-distance blue water sailing.