This article is from the CD-Recordable FAQ, by Andy McFadden (firstname.lastname@example.org) with numerous contributions by others.
You haven't closed the session yet. The lead-in area, which includes the
TOC (section (2-27)), isn't written until the session is closed. A space
is left for it that is large enough to see. Read section (2-19) for more
details on what happens when you close a disc.
You will see the narrow unwritten strip if you:
- write a disc, telling the program to leave the disc and session open.
- eject a packet-written disc without having closed it in ISO-9660 mode.
- have a failure during recording in track-at-once mode.
In some cases it's perfectly normal to see this space; it's where the
lead-in area will be written when the session is closed. It's not
necessarily a sign of failure.
If you use disc-at-once recording, the lead-in area is written right away,
so after a failure you won't see the gap.