Basically using 4 sigils of hope which completely drains my mana from 100%, then sometimes when I cast volatile reversal, it refunds all mana and immediately ticks down as if I cast another volatile reversal. I am specced for 4 seconds so it should stay at 100% mana after casting reversal.
You are right about echoes however, this seems counter intuitive. What is the benefit of echoes being able to cast sigils if they cost mana? The fact that I have to wait to cast Reversal makes me vulnerable to death because I am not channeling Warpath…