PappaJo it's sounds like the safety culture there isn't that bad seeing as these things are being reported, it's when incidents like this aren't reported and things are quiet that safety culture should begin to be questioned
I personally think this happens more than is actually reported,I just heard another carrier last week being asked by ground to check seat occupancy on behalf of their company...then a return to the bay. I blame the new automated check in and boarding procedures, and don't get me started on the security side of things.
I must admit this was a big mistake by J*( 15 pax!), would a swap from and A320 to an A321 cause this issue (or vice versa)?. Having been on one of their A321's and asked to moved seats before the doors where closed to " keep the aircraft within balance limits" I am sure the pilots are just working off the information they are given, not intentially operating out of limits.