This post is easier and shorter to read than it looks, the text is just big.
How does it happen?
The duplication glitch only happens on items with toggles. When you change the toggle of an item and save a new outfit, you might notice that the toggle reverts back to default. This is because when you switch the toggle you can't see it but it keeps two of the same items on seperately. I noticed this every time i tried to save it as an outfit.
How do i fix this?
First, unequip that specific item including the duplicates.
To fix the bug, re-equip the same item and color the toggle. Leave the toggle on the one you want, then stop wearing the same item with the toggle you don't want. It usually says the toggle number in the title if you can't tell the difference.
Example: If you wanna wear toggle 2 of the item but experience the bug, take off toggle number one, color toggle 2 and then keep it on. you must change the color of the toggle number you want or else it'll repeat and you'll have to start all over.
EXAMPLE OF THE GLITCH
NOTE: once you save the outfit with the toggle you want, you will not experience the duplication glitch with that item anymore.