First of all when admins move threads, they need to uncheck that little box that asks you if you want to leave a shadow of the thread in the forum it was first started in.
We do have some shadow threads still hanging around though and I found out the hard way yesterday that if you delete the shadow thread, you also deleted the entire thread that was moved. Crazy if you ask me, but it happens. So, if you come across a shadow thread, just let 'em be.