This has been fixed.
Patch 5.0.4 introduced an annoying bug to deal with.
Blizzard accidentally declared "_" to be global, so if your addon uses "_" as a global it will cause the GlyphUI frame to not work.
It's an easy fix, instead of:
local class _, class = UnitClass("player")
Just declare _ as a local variable:
local _, class _, class = UnitClass("player")
or you can achieve it another way using the select method:
local class = select(2, UnitClass("player"))
Using local variable over global variables is good addon practice for a variety of reasons, some of which include speed of access, interactions with other addons/Blizzard UI, and just not polluting the global namespace.
Good news however is that this is already fixed on the beta and should be slated for patch 5.0.5.