DV and FireWire are not frame accurate device control protocols. This can mean that when you capture a clip it may capture several frames early or late. The Timecode numbers will still match the frames of the media (if properly calibrated). Also, when performing an Edit to Tape function, the edit may take place a few frames earlier or later. To get frame accurate control you must have a video deck which supports a device control protocol such as RS-422, or RS-232.
Note: A USB to serial adapter must be used with RS-422 or RS-232 devices on Power Macintosh G4 computers, or any Macintosh without built-in serial ports.