When you special attack with anchor on an NPC or player, but then, while the anchor is raised in the air, click away, the special attack comes down and lands on nothing. Really cool. The problem is that it still drains special attack energy, and if you do it again, it drains more special attack energy, and again, etc.

So if you continue doing it, you actually go below the normal special attack bar parameters.

*Edit*
I found out that sometimes even if the anchor special attack lands a hit directly onto the monster, sometimes it doesn't even show a hitmark at all, not even a 0, and this creates the same scenario which originally takes out special attack bar, because it then attacks again (special) and drains even more special energy.