So a friend noticed he had less magicka on his backbar and couldn't figure out why.. after a bit of messing around we found that removing Flames of Oblivion caused magicka to return to normal.. I tested it on my own DK and found the same issue..
Without FoO (39,863 mag):

With FoO (38,242 mag):

I lose 1,621 magicka if I have Flames of Oblivion slotted. Is this a bug? Surely it can't be intended..
Guild: Just Some Guild
Ysmira - VR16 Dragonknight - AD - Former Empress [Thornblade NA Cycles 2-3]
Vanarra - VR16 Templar - AD - Stormproof
Seraffina - VR16 Nightblade - AD - Stormproof
Cellestina - VR16 Dragonknight - AD - Stormproof
Celestina Warbeck - VR16 Sorcerer - AD - Stormproof
Elleyana - VR16 Templar - AD
Freiya - VR16 Stam Temp - AD