gstvorbistag.c doesn't handle dates that include timestamps.  For example if you download the ogg version of this album:

http://www.jamendo.com/en/album/2534/

The tracks all have timestamps after the date, e.g.:

ogginfo 01\ -\ Ventus\ Solaris.ogg
Processing file "01 - Ventus Solaris.ogg"...

New logical stream (#1, serial: 6a79bd1a): type vorbis
Vorbis headers parsed for stream 1, information follows...
Version: 0
Vendor: Xiph.Org libVorbis I 20040629 (1.1.0 rc1)
Channels: 2
Rate: 44100

Nominal bitrate: 224.000000 kb/s
Upper bitrate not set
Lower bitrate not set
User comments section follows...
        ARTIST=Revolution Void
        ALBUM=Thread Soul
        TRACKNUMBER=1
        TITLE=Ventus Solaris
        DATE=2006-08-21 22:02:38
        ORGANIZATION=Jamendo : http://www.jamendo.com/
        COMMENT=Jamendo : http://www.jamendo.com/
        DESCRIPTION=Jamendo : http://www.jamendo.com/
        WWW=http://www.jamendo.com/album/2534
        LICENSE=http://creativecommons.org/licenses/by-nc/2.5/
        WCOP=http://creativecommons.org/licenses/by-nc/2.5/
        WOAF=http://www.jamendo.com/track/17954
Vorbis stream 1:
        Total data length: 10870973 bytes
        Playback length: 6m:54.730s
        Average bitrate: 209.697206 kb/s
Logical stream 1 ended

This can be fixed trivially, if you really only care about the first part (the date itself) being correct, by not checking for the terminating character:

diff -u -r1.18 gstvorbistag.c
--- gstvorbistag.c      23 Sep 2006 13:21:07 -0000      1.18
+++ gstvorbistag.c      24 Sep 2006 22:50:19 -0000
@@ -244,7 +244,8 @@
             d = strtoul (check, &check, 10);
           }
         }
-        if (*check == '\0' && y != 0 && g_date_valid_dmy (d, m, y)) {
+        if (y != 0 && g_date_valid_dmy (d, m, y)) {
+       //if (*check == '\0' && y != 0 && g_date_valid_dmy (d, m, y)) {
           GDate *date;

           date = g_date_new_dmy (d, m, y);

Although I'm not sure if this is a robust solution.  Perhaps it could parse the time as well (just be sure it's not garbage), and then ignore it.

In either case, many of the tracks (which are all Creative Commons licensed) on http://www.jamendo.com/ appear to format the date this way (and there are probably other sites that do so as well), that it would seem to make sense to be able to gracefully handle these datestamps even if they are slightly out of the vorbis spec.