The feature in question is when you click on your bags in edit mode with the dropdown box for “Direction” which lets you choose between stacking right to left, or left to right. Good for when you want to move your bags to the other side of the screen.
The UI edit mode is really inconsistent when it comes to saving your choice in this feature.
It will save, sure, and SOMETIMES it will load that change when you switch to a different character using the same UI preset, but often times it reverts back to left, which is the default.