This is an old question that I haven't asked as it only comes up once in a while, but that still mystifies (and annoys) me after all these years.
Assume that the PC has two rings equipped to his ring slots and a third in main inventory. When the player right clicks on the ring in inventory and chooses "Equip" from the radial menu, that ring is usually swapped for the ring in the lower of the two ring slots. I haven't kept track, but I would guess that it happens that way for me over 98% of the time. That's perfect game behavior in response to a player command - it's predictable and I know that when I right-click equip a ring, I will then have that new ring equipped in the lower slot, along with the ring in the upper ring slot, losing whatever benefit from equipping the ring formerly in the lower ring slot. But, once in a great while, the right-click-equipped ring will replace the one in the upper ring slot. Argh! Half of my toons are casters and swapping out that top ring means that they just lost spells because I had an casting-ability-increasing or bonus-spell-slot-granting ring in that upper slot. Moreover, I might not even realize it has happened because I often use the radial menu to equip gear when I have a container open and cannot see my equipment slots.
So, my question is: How does the game choose the slot into which a new ring is equipped when the toon already has two rings equipped? Clearly it is not totally random, because it equips to the lower slot the vast majority of the time. But, sometimes it chooses the upper slot and I would like to know if there is some predictable mechanism at work here.
BTW, I have a suspicion that the answer
But, I am curious if anyone has noodled out the exact process.
And, of course, I already know that any uncertainty can be eliminated by actually dropping the new ring onto the desired slot. I would be interested in a workaround that eliminates the rare upper-slot behavior from the right-click-equip method, but I am more interested in knowing what's really going on than in workarounds at the moment.