The problem is that the order of events firing during the loading process has changed again at least in the current PTR builds.
What I'm talking about is this.
http://wowpedia.org/AddOn_loading_pr...iables_Loading
A lot of addons have come to depend on events firing in a specific order and code as if that's a given without safeguards in place.
Assume that PLAYER_LOGIN will always fire after ADDON_LOADED for your addon so it's safe to do addon initialization at PLAYER_LOGIN etc.
Well as it happens that order is not guaranteed and is no longer the case in 5.4.
So if things don't change between the current PTR builds and 5.4 going live, addons will have to be smarter and not make assumptions on event order during the loading process.