Symptoms

The "Make available for home directories" option can be checked in Lion Server's Server.app on a server that is simply joined to a directory server, but the mount record is not actually created. After this happens, the option cannot be unchecked.

Resolution

Use the Directory Editor in Directory Utility or any other LDAP editor and create the mount record manually.

Because mount records need different attributes depending on the tools used to edit them, it is best to look at an existing record with the editor and use that as a template. The Directory Editor in Directory Utility will show a record similar to one below.

RecordName: server.example.com:/Volumes/Data/Homes
RecordType: dsRecTypeStandard:Mounts
VFSLinkDir: /Network/Servers
VFSOpts: net
VFSOpts: url==afp://;AUTH=NO%20USER%20AUTHENT@server.example.com/Homes
VFSType: url

LDAP editors will show a record similar to the one below.  Note the LDIF style line wrapping.

dn: cn=server.example.com:/Volumes/Data/Homes,cn=mounts,dc=server,dc=example,d
  c=com
mountType: url
mountDirectory: /Network/Servers
objectClass: mount
objectClass: top
mountOption: net
mountOption: url==afp://;AUTH=NO%20USER%20AUTHENT@server.example.com/Homes
cn: lion.aclab.apple.com:/Volumes/Data/HomeDirs

Note that Open Directory masters, relays, and replicas are not affected.