SMN Spell Tri-disaster Bind effect not working properly

[GinTama]

The spell Tri-disaster binds the enemy for 20 seconds upon casting it the first time. After binding it, if you attempt to damage the target, the bind effect vanishes. It's as if you cast sleep and then attack but bind should not react that way.

Since the effect of Blizzard II is bind too and there working properly, I suspect this is not working as intended.