Just a couple more data points and perhaps some tactical thoughts...

I flew COU-DFW-HKG rt a while back and applied SWUs both ways. One of them apparently caused the distance calculation, but the other didn't. No idea why, but it fits with what others are saying...various things that cause reticketing might trigger this, but might not.

Then more recently I had a flight change due to weather; instead of flying COU-DFW I had them send me STL-DFW (they wanted to send me the next day from COU, which was kinda funny given my original itinerary had me flying in/out the same day for a half-day meeting) instead. That one posted based on distance as well.

The HKG change was hugely beneficial, as I got the ticket for pretty cheap (~$750 rt) and it was quite a long distance. The DFW one, not so much...last minute ticket out of a regional airport for a <500 mile flight cost me something like $500.

But here's the nice part: given that it wasn't hard to establish what the fare was, I just called them and asked them to credit it properly, and they did. And obviously, I never mentioned anything about the HKG flight.

So...the point here is that if you're paying attention you can get these fixed when they're in AA's favor and leave them wrong when they're in your favor. This could be pretty beneficial, particularly for those who tend to have a lot of reticketing activity.

Now if we could just pin down causes with a bit more precision, and maybe even figure out some reliable ways to trigger......