I'm disappointed to see that the web archives are showing the attachments in exactly the opposite order. That could confuse someone no end ...
In fact, it was completely unordered - the query that listed the attachments had no ORDER BY at all. Not entirely sure why but that seems to have more or less always returned them in the reverse order.
I've added an ORDER BY on the serial column that the attachments get their id from, which should make it always sort them in the same order as they were inserted. As usual, it'll take a few hours for the effects to show through the caching.