Alright, turns out I was wrong (which is good!)
I have a replay demonstrating the bug in action, and it is a game-breaker in that if it happens to you it heavily punishes you depending on what happened.
Since you can't see my clicks in replays, here are my steps to reproduce:
1- Select a General
2- Purchase any idol (I've been using siege gunners)
3- Summon the idols
4- Sell them using the cooldown-idol glitch I reported earlier today
5- Wait for 30 seconds for your cooldown timer to expire
6- Resummon idols, watch it "fizzle"
7- Open up the shop menu, and click Trinkets, then Narmoth's Ring. Then Armor and then Banded Armor
8- Right click the Siege Gunner symbol on your dashboard
Nothing should happen, you're attempting to sell a non-existent item
You sell your Narmoth's at it's refund value. (or whatever item you first purchased when you opened the shop dialog, if you had existing items already there)
What I thought was happening, initially, was you're selling the item you most recently purchased at the refund value of your idols. This could mean you could resell Scailmail at say, 1800 with Demolishers.