As seen in the above video (dated September 7th 2012.) some players (including myself and the creator of the said video) are experiencing a bug which prevents the usage of the skill 5 in water attunement elementalist staff skillset.
The said problem is (judging by some comments) fixable by repeatedly killing stuff with water attacks, thus “reunlocking” the skill, which was already unlocked. That doesn’t seem like much trouble to do but it would be nice to get a fix for this.