What’s actually strange with this is that it’s a double-reversal: the links themselves are reversed, and the rollup then “corrects” the problem with the links.
In a test I ran recently, I made a table with these items in the primary field:
I then linked each record one by one to a control table. When looking at that table’s link field, they’re in reverse order. When using a rollup to pull data from that linked table, it reverses the order again, so they’re back the way they belong:
I suppose the point I’m trying to make is this: if you create the original links in the order that you want them in the final rollup, they’ll stay that way through this double-reversal process.