i'm trying to upgrade a 7.2.2 foss to 8.0.2 and its failing at the point of ldap migration with:

5126fc9e olcAttributeTypes: value #0 olcAttributeTypes: Duplicate attributeType: "1.2.840.113556.1.2.146"
5126fc9e config error processing cn={4}zimbra,cn=schema,cn=config: olcAttributeTypes: Duplicate attributeType: "1.2.840.113556.1.2.146"
slapadd: bad configuration directory!

i believe whats happening is there's 2 zimbra.ldif's at the point of migration:
root@server:/opt/zimbra/data/ldap/config/cn=config/cn=schema# ls -l
-rw------- 1 zimbra zimbra 3316 2013-02-22 00:05 cn={3}dyngroup.ldif
-rw------- 1 zimbra zimbra 445851 2013-02-15 00:38 cn={3}zimbra.ldif
-rw------- 1 zimbra zimbra 30213 2013-02-15 00:38 cn={4}amavisd.ldif
-rw------- 1 zimbra zimbra 551442 2013-02-22 00:05 cn={4}zimbra.ldif
-rw------- 1 zimbra zimbra 33138 2013-02-22 00:05 cn={5}amavisd.ldif

is this supposed to be this way? i found this appears to happen with a call to "zmldapschema" during the upgrade, which copies over the {4}zimbra.ldif and {5}amavisd.ldif - so when zmslapadd is run, it dies on the second zimbra.ldif (i think!?).
Is zmldapschema supposed to be over-writing the files that are already there (looks like it does with the core/cosine/etc)? if so - would i be correct in saying i should rename the zimbra and amavisd files just before that step is run so that they too get overwritten?

i'm just not comfortable with ldap yet so i'm not sure what all is happening with migration, etc.