Description of problem:
Steps to reproduce:
1) set up MMR

2) create a subtree in the database
dc=example,dc=com
         |
    ou=orgunit0
    |          \
ou=orgunit00  ou=orgunit01
    |            \
uid=tuser000  uid=tuser010
uid=tuser001  uid=tuser011

Delete ou=orgunit0

3) shutdown the server

4) export the backend:
   # /usr/lib[64]/dirsrv/slapd-ID/db2ldif -n userRoot -r

5) import the exported file
   # /usr/lib[64]/dirsrv/slapd-ID/ldif2db -n userRoot -i /path/to/ldif/file
[..] - import userRoot: Processing file "/var/lib/dirsrv/slapd-kiki0/ldif/kiki0-userRoot-2011_12_12_172236.ldif"
[..] - import userRoot: Finished scanning file "/var/lib/dirsrv/slapd-kiki0/ldif/kiki0-userRoot-2011_12_12_172236.ldif" (18 entries)
[..] - import userRoot: WARNING: Skipping entry "nsuniqueid=ceb8df01-252711e1-856cfebb-9066bfc6,ou=orgunit00,ou=orgunit0,dc=example,dc=com" which has no parent, ending at line 201 of file "/var/lib/dirsrv/slapd-kiki0/ldif/kiki0-userRoot-2011_12_12_172236.ldif"
[..] - import userRoot: WARNING: Skipping entry "nsuniqueid=ceb8df02-252711e1-856cfebb-9066bfc6,ou=orgunit01,ou=orgunit0,dc=example,dc=com" which has no parent, ending at line 218 of file "/var/lib/dirsrv/slapd-kiki0/ldif/kiki0-userRoot-2011_12_12_172236.ldif"
[..] - import userRoot: WARNING: Skipping entry "nsuniqueid=ceb8df03-252711e1-856cfebb-9066bfc6,uid=tuser000,ou=orgunit00,ou=orgunit0,dc=example,dc=com" which has no parent, ending at line 240 of file "/var/lib/dirsrv/slapd-kiki0/ldif/kiki0-userRoot-2011_12_12_172236.ldif"
[..] - import userRoot: WARNING: Skipping entry "nsuniqueid=ceb8df04-252711e1-856cfebb-9066bfc6,uid=tuser001,ou=orgunit00,ou=orgunit0,dc=example,dc=com" which has no parent, ending at line 262 of file "/var/lib/dirsrv/slapd-kiki0/ldif/kiki0-userRoot-2011_12_12_172236.ldif"
[..] - import userRoot: WARNING: Skipping entry "nsuniqueid=ceb8df05-252711e1-856cfebb-9066bfc6,uid=tuser010,ou=orgunit01,ou=orgunit0,dc=example,dc=com" which has no parent, ending at line 284 of file "/var/lib/dirsrv/slapd-kiki0/ldif/kiki0-userRoot-2011_12_12_172236.ldif"
[..] - import userRoot: WARNING: Skipping entry "nsuniqueid=ceb8df06-252711e1-856cfebb-9066bfc6,uid=tuser011,ou=orgunit01,ou=orgunit0,dc=example,dc=com" which has no parent, ending at line 306 of file "/var/lib/dirsrv/slapd-kiki0/ldif/kiki0-userRoot-2011_12_12_172236.ldif"
[..] - import userRoot: WARNING: bad entry: ID 12
[..] - import userRoot: WARNING: bad entry: ID 13
    [...]
[..] - import userRoot: WARNING: bad entry: ID 16
[..] - import userRoot: WARNING: bad entry: ID 17
[..] - import userRoot: Workers finished; cleaning up...
[..] - import userRoot: Workers cleaned up.
[..] - import userRoot: Cleaning up producer thread...
[..] - import userRoot: Indexing complete.  Post-processing...
[..] - import userRoot: Flushing caches...
[..] - import userRoot: Closing files...
[..] - All database threads now stopped
[..] - import userRoot: Import complete.  Processed 18 entries (6 were skipped) in 5 seconds. (3.60 entries/sec)