While investigating a problem of writing to a mounted samba share I came across this. It looks odd as the standard tc user appears to belong to different groups, depending upon how the question is asked.
List groups as user tc
tc@box:~$ id
uid=1001(tc) gid=50(staff) groups=50(staff),1000(audio)
List groups as user tc specifying user tc
tc@box:~$ id tc
uid=1001(tc) gid=50(staff) groups=50(staff),1000(audio)
Create a group and add user tc to the group
tc@box:~$ sudo addgroup -g 2001 testgroup
tc@box:~$ sudo addgroup tc testgroup
List groups as user tc
tc@box:~$ id
uid=1001(tc) gid=50(staff) groups=50(staff),1000(audio)
List groups as user tc specifying user tc
tc@box:~$ id tc
uid=1001(tc) gid=50(staff) groups=50(staff),1000(audio),2001(testgroup)
Is this normal and expected behaviour?