[Dovecot] Permission problem with LDA and dovecot 2.2.1

[Tobi]

Hello list

today I built dovecot 2.2.1 from sources. But I have permission problems 
with LDA
The "normal" imap part works fine, users can login and see their boxes.
deliver is called as LDA from postfix master.cf as follows
<<
dovecot unix    -       n       n       -       -       pipe
  flags=DRhu user=vmail:vmail argv=/usr/local/libexec/dovecot/deliver -f 
${sender} -d ${user}@${nexthop}
 >>
but when I try to send a testmail then I get the following in the logs

<<
2013 May  6 18:37:59 nordkap lda: Fatal: Internal error occurred. Refer 
to server log for more information.
May  6 18:37:59 nordkap dovecot: lda: Error: userdb lookup: 
connect(/var/run/dovecot/auth-userdb) failed: Connection refused
May  6 18:37:59 nordkap dovecot: lda: Fatal: Internal error occurred. 
Refer to server log for more information.
 >>

For me it looks odd because the auth-userdb is defined as
<<
base_dir = /usr/local/var/run/dovecot/
service auth {
   unix_listener auth-userdb {
     mode = 0777
     user = vmail
     group = vmail
   }
....
 >>

The rights on the file should be correct according to the config above
<<
ls -al /usr/local/var/run/dovecot/auth-userdb
srwxrwxrwx 1 vmail vmail 0 May  6 20:11 
/usr/local/var/run/dovecot/auth-userdb
 >>

I cannot explain why the lda tries to access
<<
Error: userdb lookup: connect(/var/run/dovecot/auth-userdb)
 >>
I grepped through all the configfiles but could not find the "wrong" 
path from the error message above.
Would it might be a "fix" to symlink /usr/local/var/run/dovecot to 
/var/run/dovecot ? Or would that break something with dovecot?

Thanks for any hint or idea

tobi