Depends.

Items get sent around all the time. In-network, copies are interchangeable, and the system balances them out among the libraries. AFAIK there's no particular need for a copy to go back to the same shelf, so it doesn't happen.

If no-one is looking for a certain item, it wont move again unless someone asks, or if the library needs space for something else.

It's kinda nice. Every time I visit a library it can have an entirely new selection. With recent requests to that location which have been returned again, or just returns, appearing on the shelves.