Word of Pain Glitch?

[Shiagur]

I got a bit of a mystery going on with my level 12 cleric. I could definitely use some insight because I feel like it's just me overlooking something incredibly obvious. Help prove that I'm an idiot please? :}

Whenever I cast Word of Pain, sometimes it will cast (complete animation) and use up mana, but not actually do any damage to the mob. It's not an interrupt and there's nothing special or different about the mobs I'm casting it on (just orcses in Crush). I don't think it's a resist, because I'm not getting a message for it. In fact, I'm not getting -any- message for it beyond the cast message. I checked my chat settings and all spell messages are going to one window so I don't think I'm missing out on anything.

Thanks in advance!