sup does not synchronise from local mbox?

[inktrap]

Hi,

maybe I am missing something, but I am currently testing sup with a local mbox. I added this mbox like it is stated in the docs, sup-add mbox:/var/mail/vh and this is the result (I only changed the format for labels from [] to -):

- !supmua.org,2006-10-01/Redwood/MBox
  uri: mbox:/var/mail/vh
  usual: true
  archived: false
  id: 6
  labels:
  - box_vh
- !supmua.org,2006-10-01/Redwood/SentLoader {}

Then I polled via P and some messages showed up in my inbox, with the correct tag. Then I quit sup and sent myself a test message:

echo foobar | mail -s "lalala" "$USER@$HOST"

However, sup-sync does not find something new:

vh@box ~ [i] % sup-sync mbox:/var/mail/vh
Scanning mbox:/var/mail/vh...
Scanned 0, added 0, updated 0, deleted 0 messages from mbox:/var/mail/vh.
[2015-11-21 00:29:12 +0100] Flushing Xapian updates to disk. This may take a while...

But the mail command which reads from the mbox finds the messages:

vh@box ~ [i] % mail
Mail version 8.1.2 01/15/2001.  Type ? for help.
"/var/mail/vh": 7 messages 7 unread
>U  1 vh@box             Sat Nov 21 00:02   17/398   lalala
 U  2 vh@box             Sat Nov 21 00:14   17/398   lalala
 U  3 vh@box             Sat Nov 21 00:14   17/398   lalala
 U  4 vh@box             Sat Nov 21 00:14   17/398   lalala
 U  5 vh@box             Sat Nov 21 00:14   17/398   lalala
 U  6 vh@box             Sat Nov 21 00:14   17/398   lalala
 U  7 vh@box             Sat Nov 21 00:20   17/398   lalala
& 

What am I missing? If I open the mbox with an editor, the mail is there.