I noticed too (post facto). Array.sort_array wasn't as well documented though, but shares the property.
/ Johan Sundström (folkskådare)
Previous text:
2003-04-23 16:12: Subject: sort
URL:http://pike.ida.liu.se/generated/manual/modref/ex/predef_3A_3A/sort.html
Note
The sorting algorithm used is not stable, ie elements that are equal may get reordered.
/ Marcus Comstedt (ACROSS) (Hail Ilpalazzo!)