Orphaned physmessages, partlists, mimeparts

hello again ;)

on my production server with dbmail 3.0.2 a run of dbmail-util always 
reports the following:

# dbmail-util -ay

Repairing DBMAIL message integrity...

Repairing DBMAIL physmessage integrity...
Ok. Found [1] unconnected physmessages.
Ok. Orphaned physmessages deleted.

Repairing DBMAIL partlists integrity...
Ok. Found [1] unconnected partlists.
Ok. Orphaned partlists deleted.

Repairing DBMAIL mimeparts integrity...
Ok. Found [1] unconnected mimeparts.
Ok. Orphaned mimeparts deleted.

so it finds some unconnected stuff and deletes it.

but if i run the dbmail-util again it always reports back the same 
message above.
so the orphaned physmessages, partlists, mimeparts never seem to get deleted

but i know, it's dbmail version 3.0.2

so on my development machine i copied the database, installed dbmail 
version 3.1.17
run the mysql migrate scripts 3_0_2-3_1_0.mysql and dbmail-util -ay
which cleaned up lots of stuff.

if i now run dbmail-util -ay

Repairing DBMAIL message integrity...

Repairing DBMAIL physmessage integrity...
Ok. Found [0] unconnected physmessages.

Repairing DBMAIL partlists integrity...
Ok. Found [18] unconnected partlists.
Ok. Orphaned partlists deleted.

Repairing DBMAIL mimeparts integrity...
Ok. Found [0] unconnected mimeparts.

Repairing DBMAIL headernames integrity...
Ok. Found [0] unconnected headernames.

Repairing DBMAIL headervalues integrity...
Ok. Found [0] unconnected headervalues.

Deleting messages with DELETE status...
Ok. Messages deleted.

Repairing DBMAIL for rfcsize field...
Ok. Found [0] missing rfcsize values.

Repairing DBMAIL for cached envelopes...
Ok. Found [0] missing envelope values.

Repairing DBMAIL for cached header values...
Ok. Found [0] un-cached physmessages.

Setting DELETE status for deleted messages...
Ok. Messages set for deletion.
Re-calculating used quota for all users...
Ok. Used quota updated for all users.

Removing aliases with nonexistent delivery userid's...
Ok. Found [0] dangling aliases.

Vacuuming and optimizing database...
Ok. Database cleaned up.

Maintenance done. No errors found.

leaves me with

Repairing DBMAIL partlists integrity...
Ok. Found [18] unconnected partlists.
Ok. Orphaned partlists deleted.

so no more problems with physmessages and mimeparts, but always reports 
orphaned partlists

i can run this again and again and the orphaned [18] unconnected 
partlists never get deleted

is this something i need to worry about? is this something i can fix 
with phpmyadmin and a custom sql query?
or is this perfectly okay?

thanks a lot for your help!

greetings
becki