Have you have ever run into problems cutting something from your sequence and not being able to paste it in the track you want to?  To copy from one track and paste to another, you need to turn off the Auto Select control for the tracks below the track you wish to paste to. For example, if you copied a clip from V1, and you wanted to paste it into V3, you would need to turn of the Auto select controls in V1 and V2. This will force Final Cut to paste into the first available track. Another way to go about this is to Option click on the Auto Select control of the track you wish to paste to. This will cause the track you Option clicked to become the only one turned on. Keep in mind if you are copying a linked clip, FCP will paste either to the same track they came from if the auto select for that track is not turned off. In other words you need to assign a destination track for both Video and Audio before you paste.