If you have two of the same weapon equipped in LD, you aren't able to scroll between them. At all. Just doesn't work. Using scrollwheel or hotkeys, it just treats it as if you have no other weapons available.
If you have 3/4 slots and have another weapon, you can cycle from 1, to the 3rd weapon, then to the twin, but it seems to react strangely to it, and sometimes just won't let you switch to them properly. It just doesn't work right.
It works absolutely fine in the CWs and any PvE area I've tried with it, but as soon as you hit LD it just totally crashes out. This is quite distressing to me because I just made a new weapon, thinking it was working fine from the CWs, but now in LD it's just not working anymore.
Any different from http://forums.spiralknights.com/en/node/69112 ?