full mana on a resist?

[Crabster]

i always thought if u failed something then it took half of the mana required to land it??

[HP=317/MA=84]:stun ba
*Combat Off*
You attempt to cast song of stunning on huge basilisk, but the spell is resisted
!
[HP=317/MA=60]:a
*Combat Engaged*

[Gardner Denver]

Itsa bug.