I don't remember changing any of my personal preferences, but when I look at my contributions (Special:MyContributions) the list starts with the earliest edits and there's no way to reverse the order. (The watchlist, on the other hand, still looks the same to me)
Topic on Project:Village Pump
Things are back to normal, so the (temporary) changes must have been restored.
Just for information: This was a bug in new MediaWiki 1.24wmf20 tracked in bug 70413. It was hot fixed for mediawiki.org and testwiki yesterday :) So that's why all is ok now :)
Alright, thanks for the explanation.