This is not just a good suggestion, this is the literally the answer.
I can only assume the north stand is hard to segregate? (Both sets of fans would be sharing toilets or something?)
And if, hypothetically, that is the case, who the hell cares?
It's the Saints Versus United, not an old firm game. We are two sets of fans who live up the road from each other and for the most part have respect for each other.
If this is the reason for the peculiar seating arrangements, the SFA really don't have a clue.
I've just realised... I've said 'the SFA dont have a clue' 100 times this season. I should get a prize.