10.4 ODM, 10.3 Directory connected server

Hi, We came across a slightly odd one last night and wondered if anyone could comment/help. We were busy migrating our ODM and replicas to 10.4 boxes that had been prepared and tested in advance. All was going well until we tried to connect the only remaining 10.3.9 fileserver we have. At that point we found that this particular server was only able to see a small subset of all the users. Does anyone know if there are any known issues or gotchas with setting 10.3 servers to 'Connected to Directory System' when the ODM and replicas are all 10.4? Cheers Dan