A strange U B da Judge Problem

E/W vul, IMPs, short matches

	KQ9x QJ109x 10 xxx
Axx Ax Kxxx Axxx		J10x Kxx AJxx QJ10
	7xx 8xx Q876 Kxx

I don't know who held the 9.

The auction was utterly insane:

North	East	South	West
2	Pass	2	Dbl
4	5	Pass	Pass
5	Dbl	All Pass

2 was supposed to be a weak two bid.
2 was natural and forcing for one round.

The defense slipped...N/S -1400.

a) Apportion the blame between North and South.
b) Which was the least idiotic bid (not pass) N/S perpetrated?