iTunes 11.0.4 still copying files to media library after dragging and dropping while holding down "option"

I'm having trouble adding media without automatically copying the file to the iTunes media libary after dragging and dropping while holding down "option."

In Preferences > Advanced, "Copy files to iTunes media folder when adding to library" is checked. When I drag a file into iTunes while holding "option", the green "plus" icon disappears. However, iTunes still copies the file to media folder.

Any suggestions?