Greetings.
I have uploaded new versions of the menu extension and the dual wield plugin that corrects this issue.
In the case where the actor is using two exactly identical weapons, and the dev is not using independent weapons from ItemCore, there is now a special case where a temporary object is created in $dataWeapons, which is used as a placeholder for one of the weapons when these checks are being made. After the calculations are done, the fake weapon is replaced with the original, and then it is removed from the database. This corrects the display issue on the menu scene, as well as the same issue in battle during split attacks, which you didn't report, but was caused by the same root cause as the display problem.
Check them out and let me know that everything is working for you.