Spooncraft

Stuff like the Onyxia buff or the one you would get from Sayge in the Darkmoon Faire would wipe if you logged or zoned. Blizzard doesn’t really want that to happen but at the same time they don’t want you to go into an instance with those buffs.

We are aware of this issue, it was caused by a change to several zone-wide buffs (such as the buffs from killing onyxia).

These buffs will be changed in the next patch to be removed only when zoning into a raid instance. (src)