RegisterUnitEvent seems bugged, simple test code:
Lua Code:
/run local f = CreateFrame("Frame");f:RegisterUnitEvent("UNIT_POWER_BAR_HIDE", "player");print(f:IsEventRegistered("UNIT_POWER_BAR_HIDE"));
IsEventRegistered return values on Live: true player
IsEventRegistered return values on Beta (26491): true
I don't know if it has been like this in the previous builds aswell, just stumbled upon it when updating some addons.