If you right click a weapon that has an available special attack, then hit F5, and quickly select the “equip” option, then try to activate a special attack, the game will state: “This weapon has no special attack!”
However, clicking on the special attack bar shortly after this message is sent results in the successful execution of a special attack.

I created this topic in response to Zezimapk's topic, since I can't reply. I think you will find that this is the same problem he/she experienced with the dragon dagger.