A Steam Workshop item has been pulled due to being a direct copy of a mace from the game Aion. Valve implemented the Steam Workshop to encourage creativity and innovation, adding a level of personalization to a plethora of games in a way that has never been done before. The publisher takes a hands-off approach to the submission process, depending on the "community to ensure originality." Currently, all contributors have to promise that their submissions are original and a system is in place so other users can report copies and plagiarisms.
From the official statement:
"This has worked great for content that exists only on the Workshop, but it becomes more complicated if a Workshop item becomes offered for sale on Steam or in a game, and the item later turns out to infringe on someone else’s work.
"We recently had an example of this problem. A user submitted a mace for Dota 2, and based on strong community ratings, the mace was made available in the game as “Timebreaker” in Sithil’s Summer Chest. 24,603 users spent money on keys to open the chest and ultimately receive the mace. Recently it came to our attention that this mace was in fact a copy of a mace from the game Aion. The copying has had negative consequences for everyone involved: users lost the mace and received an alternative weapon instead, the contributor has been banned and will lose out on any proceeds from the sale of the item, and it took a lot of time for us to investigate and remedy the situation."
It sounds like Valve is going to continue allowing the community to police itself. Hopefully, this problem doesn't arise again in the future.