Accidently duped stuff?

I took out 6 legendary willow from my storage by right clicking and taking 6 then traded to a guildmember of mine, went out did some herbalism, after reset at 18:30 26 of november i logged back in and checked my storage to find i had gained the 6 willow back.
I don't know the steps I did to dupe, just know somehow it happened.