I too have had trouble with this. If you paste multiple copies it can get very confusing. One procedure I developed: If you want to copy a section of track, select the section and copy. Don't past right away. Move the original section to the new location. The original location will be empty. Then hit paste and the copy will be placed in the original location. If there is a mistake and there have been multiple pastes, this will be revealed by the original location not being empty after the move.
Bill