When dual wielding Grave Calling with another open, the freezing lash gets applied to both of them. I know that there has been a history of this bug happening with other weapons in the past but I know that some of the occurrences have been fixed (for example Modwyr). As of patch 3.0 this still happens with Grave Calling, so not sure if this is intended or not. If intended the description of the ability should be updated to differentiate it from the other cases (like the example I provided with Modwyr).