It's a text error.
Disruption Arrow works great. You can tell which mobs are affected because they get a red shield effect graphic (and they die very quickly ).
I really should do something about this signature.
Its been there since..uh..forever?
As PRAF68 says, text error is all that it is, that in no way effects you.
Unless you count that annoying message every time you use it. ^^
@Inkwave ..(darn merge)
So, I'm soloing my level 19 trick arrow defender Swallowtail, and for once I happen to have the combat tab on top. Goes up against some clockwork and fires off Disruption Arrow, and the following flashes up on the screen:
"Your Disruption Arrow reduces the resistances of Swallowtail"
Say again? This message has to be an error -- Disruption Arrow can't actually affect the good guys too, can it? I don't seem to be taking any more damage with DA fired than without, at least.