For example in this gif he uses bobbing or weaving 20 times. The skill costs 9 mp, so it should've used 180 mp, but it used 945 mp. That's a 5.25x more mp! This is a really bad bug for blasters especially for bosses with a potion cool down because you'll drain so much mp in seconds. I drained about 7000 in 10-30 seconds!
In this video, the blaster drains way less mp compared to the gif and he is using other skills which should drain more mp than the gif.