I’ve been using the same weapon with the same enchant for a couple of weeks. Each time I run a Best in Bags with an import, Mr. Robot suggests that I apply “Deadly Navigation” to my offhand weapon when its already enchanted with Deadly Navigation.
I would have to see your whole setup – if you press the “help” link up by the big Best in Bags title, it opens a window with a button that says Create Support Post. Press that, and copy the snapshot ID here, then I can try out your setup.