You know how when you have the AH up and you can right click something from your inventory and it pops that item into the sell window? Yeah, don’t do that with a consumable flask or potion. 
Yeah, it’s worked that way for a long while. That’s the method I use for tokens and crafted items constantly. Good news, you can cancel the auction but lose the deposit. Unless you realized too late and someone else is drinking your potion.
What I mean is, if you are in the AH and right click a potion thinking you will sell it, you instead consume it. My rogue alchemist just tried to right click to sell a healing pot and drank it instead.
OH! I have never sold consumables like that.
Were you on the sell tab?
No. But for non consumables, you don’t have to be on that tab. You just have to open the AH window and right click and it automatically goes to the sell tab placing the item in the sell slot.
This is why I always make sure I’m on the sell tab when selling now, regardless.
Once upon a time, I lost out on 500k gold back during Legion when I wasn’t on the sell screen and didn’t realize it. I right clicked on a Pocket Fel Spreader toy. RIP me. 