Microsoft Knowledge Base Article 314649 contains the following summary:
The Microsoft Exchange 2000 schema defines three non-Request for Comments (RFC)-compliant attributes: houseIdentifier, Secretary,
and labeledURI. The Microsoft Windows 2000 InetOrgPerson Kit redefines the Secretary attribute and the labeledURI attribute.
The adprep /forestprep command in Microsoft Windows Server 2003 has redefined all three attributes as described in Request for Comments
If Exchange 2000 created these three attributes before you ran the Windows 2000 InetorgPerson Kit, the LdapDisplayName attribute for the houseIdentifier attribute becomes conflicted or "mangled" after the new RFC-compliant definitions are added by Windows Server 2003 adprep /forestprep replication. If Exchange 2000 created these three attributes before you ran the Windows Server 2003 adprep /forestprep command, all three attributes become mangled. These conflict do not occur if the Windows Server 2003 adprep /forestprep command creates these attributes before you install Exchange 2000.