[PC - Steam] Can't multi-weapon Resurgir Dagger+Wire

I'm trying to multiwep my Resurgir Dagger and Resurgir Wire (both unlocked in inventory) but when I try to choose either from Base Item Selection, the other one does not appear in Material Item Selection (just says "No weapons"). Any ideas on why this is happening? Bug or by design?

You need to have the fodder weapon un-equipped to merge it with the base, it doesn't matter if the base weapon is equipped or not.