OK, so i toyed around some more and can get it working if i go into my mouse application (X Button Mousecontrol) and click apply, though it's strange that i have to do this when it's already applied normally. Before i do that, Octopus picks up my middle mouse button as my left button.

So i'm still stuck trying to get Octopus to recognise my middle mouse button as middle mouse button, instead of thinking it's the left mouse button when i click it. The above thing isn't a solution cause it requires me to do this every time i alt tab and such.

Edit - I'll try installing the mouse filter, not sure if this will help at all though. I assume from the instructions it won't make a difference with WoW.