https://mods.curse.com/addons/wow/extraquestbutton?comment=18

There seems to be a bug that occurs when a quest item has the same name as a toy (and perhaps other things). This is my guess at what's happening, anyway.

I ran into the problem while doing the quest The Mantidote. When I used the keybinding to use the quest item, it worked once (and once again many minutes later) and then it kept saying the item wasn't ready despite it clearly not being on cooldown; the icon showed it was ready (and the item doesn't have a long cooldown to begin with). The quest item is Ken-Ken's Mask, which has the same name as a Toy that has a long cooldown.

It seems like it was trying to use the toy instead of the quest item or something (though the quest item was used at the same time? or the quest allows you to use the toy instead of the quest item? I don't know for sure).

If I dragged the quest item to my bar and clicked that or used Blizzard's small quest item in the watch frame, I didn't have this problem. It only happened with the keybinding (and presumably the button) from this addon.