I encountered this with a friend who had a "Thriller" attachment, that would make you dance to Michael Jackson's hit of the same name while playing the song. It was chat activated and chat de-activated. However, after she detached it at some point, somehow it remained. However, it no longer listed as an attachment in either her inventory or her Edit > Detach Object menu, which made it impossible to detach in that way. The strangest thing was this: the prim was not attached to her body. It appeared at the moment she tp'd or entered a sim, but would then stay where it was, no matter where she went, until she left the sim. The snag, of course, was the attachment prim was both transparent and extremely small in diameter, so it could only be detected with extreme difficulty. I finally managed to pinpoint it due to the particle effects that scripts give off when they chat and after I showed her where it was, she could detach it by right-clicking the prim. Unfortunately I could not reproduce this with the attachment (I received a copy), nor had I, or anyone I knew of, heard of it. I also could not find that issue here, so I fill in this report, so that other people might respond to it and give you a more solid testing base.