It appears that you need to fixate, even in the case you describe. Failing to do so caused my DVD drive to remain busy until I reset the machine.
The DVD formats other than DVD-RAM, even the so-called `RW' formats, really don't fit the old block-device model. The RW formats require an erase pass, then a sustained-burn pass, ending with fixation. The R formats don't require the erase pass, but aren't rewritable. DVD-RAM actually does permit seeking to and rewriting individual sectors and doesn't require fixation; it's much more rational for storing data (and copes better with errors than DVD+, which copes better than DVD-).
