[hinoko11]

   
   

As the image above, you are able to equip an identical class badge by having both the normal version and the plus version of a badge and equipping both of them.
While this is not mechanically sound as it seems, this does allow destiny builds to gain +12 skill slots by equipping both badges - which a lot of destiny builds desperately need.
This bug seems to be applicable for all direct upgrade items, though I would need to validate that if needed.

I have experienced and heard equipping the normal and plus version of upgraded items such as the Swordmaster's ring+ and normal are supposed to be something that can be done, and my build greatly appreciates being able to have more skill slots than the stats allow, so if this can be kept in it would be nice! 

But otherwise, it is using an item that has been upgraded and has mostly the same effect with the original item. If it is considered using a duplicate of the same accessory, it'd need to be fixed.

[Autumn]

I mean it sounds like to me they're different accessories, upgrades or not, nor is there any harm in allowing them to remain this way at the current moment.

[hinoko11]

Honestly, I'd love to keep it, it's what makes that char play the 'Monk' part of the build without Monk being a 'STR WIL CRIT KIWOKEN FP REGEN' stat stick.
Even with the +1 to skill for both badges, FP cost reduction is not the biggest role, and removing the ability for certain destinies to save guile and will to get more skill slots would be very lovely.
However, it's a bug, it had to be mentioned.

[Neus]

This has been corrected in 3.03 v6.