I vaguely recall one telling of it that noted the problem wasn't simply due to square windows, but some other contributing factor, an adjustment to the design t

I vaguely recall one telling of it that noted the problem wasn't simply due to square windows, but some other contributing factor, an adjustment to the design that caused extra stress on top of the corners. An opening on the top for a radio receiver was improperly riveted, instead of being glued. The rivet holes caused stress concentration, which resulted in metal fatigue and eventual failure and explosive decompression. When this root cause was discovered, it was also realized that the window corners also caused stress concentration.