Not a bug.
You have several conversions of same damage type that work simultanously.
Aether damage to AAR from Mythical Clairvoyants Wand converts to cold, and Fire damage from AAR converts both to cold from Conduit and Aether from wand.
Fire damage to AAR from medal Mark of Ulzuin converts to cold, and Lightntng damage from AAR converts both to cold from Conduit and Fire from medal.