Blood mage mana bug

Im still somewhat new to the game so i might be reading the descriptions wrong but my blood mage will go periods only consuming life as a resoirce for spells but then for curses or soul offering she will use both life and mana which i believe shouldnt be the case. And as the writing of this post my blood mage is now consuming both life and mana for all spells. Another thing i have noticed which i dont think its supposed to be the case, is that, when you drain your mana (rare's modifiers or body over mind keystone) you are unable to cast any spells even though you should only rely on life for spells.