Okay, once more. I need to work on my explanations.
The event is never registered at all. This is especially troubling with AceEvent, because after it thinks it registered it, it will not try again for any subsequent addons yet it will never receive any calls to pass on to the addons.
And also remember that this is not necessarily in your addon. If you are registering the event and someone else is loading the addon and you both use Ace, there is a chance that you will be affected.
indeed, i was breaking auctioneer by trying to load it during an ADDON_LOADED event in lsw.