I noticed the dirt set doesn't seem to have one-way down arrows in it.
I assume this to be an oversight, since the auto-downloadable tileset rules state
One-way arrows: If the set contains any direction of one-way arrows, it must contain all 3 directions.
Here is proof that they aren't in the object list.
It will not scroll down further than this, so if they're there, then there's something wrong with the object window.
I suppose it's possible I have an outdated version of the set somehow, but I'm not sure how that would have happened.
I checked the other tilesets from the original games and did not find any others that were missing them, excluding Christmas, which doesn't have one-way arrows at all.