The timing on volatile reversal does not seem to be consistent.
Taking the +2 second nodes to make it 4 seconds of reversal does not always put you back to where you were 4 seconds ago.
I feel when using warpath the time does not count correctly , resulting in it failing to restore any mana or putting you at a point where you had less then you ever did in the last 4 seconds. This is more noticeable in arena where the fights can last a while.
It also does not seem to count properly when disengaged from battle for me sometimes.
another issue could be using volatile too quickly in an arena fight , possibly putting you to negative time and very low mana.