Filesystem dump incremental?

[Matthias Petermann]

Hello,

currently I am experiencing something confusing. Some hours ago I did a 
level 0 dump with the following command:

     dump -a -0 -f /mnt/da0/backup-compaq.0.dump /

This results in a quite big dump file. After changing a couple of files, 
I tried to do another dump. This time as level 1. My expectation was 
that the resulting dump would only contain the files which changed since 
the level 0 dump.

     dump -a -1 -f /mnt/da0/backup-compaq.1.dump /

To my surprise this seems to generate another full dump instead of 
incremental.

What did I miss or what mistake do I make?

The filesystem is mounted with the following options: ufs, local, 
journaled soft-updates

Regards,
Matthias