From the aforementioned 1962 Le Cycle, by D. Rebour on the technical side of the Tour de France:
"In fact, there were some Italian cranks made from light alloy that broke. In my opinion, this is due to the material used in a particular series, no doubt by the subcontractor who supplied the raw forgings, who might have mistakenly used an alloy that is too "dry," and not the one usually used, which until now, had given perfect satisfaction.
Knowing how reputable this brand is, without a doubt the necessary has already been done, but it is very difficult to retrieve a defective series after quality control could not detect this hidden flaw.
Perhaps, if the manufacturer had retained the original cross-section (of the crank arms), this problem would not have occurred.
But it is obvious, that because of demands of the racers, who always want to reduce the width of the pedaling (what we call Q factor today), the manufacturer was moved to reduce the thickness of the cranks by 2 mm. Even though the wise decision was taken to augment the width of the part by the same measure, the reduction was made in the direction of the maximum load, where flex can occur when the pedal is pushed. I think it would be good to return to the original cross-section.
This does not keep us from admiring the precision and finish of the Campagnolo cranks, and also remark the perfect record of the Stronglight cranks and TA rings."
Translation Jan Heine (rough, sorry, no time to polish). Translator's notes in parentheses.
Source: Le Cycle, July/August 1962, p. 33
Jan Heine, Seattle