We have a 6.X setup running for quite a while (but not servicing requests yet) which will replace the current 5.X setup. In order to keep data current we have the primary 6.X master acting as a consumer of the 5.X master. We ‘ve run into the same problem many times and it seems that 5.X and 6.X act differently when adding an entry with empty RDN (something like uid=, ou=people, dc=<domain>). 5.X will allow the entry to be added while 6.X will reject it. The end result is that every time an entry like that is added (mostly by mistake) in the 5.X infrastructure, replication to the 6.X servers is halted and we need to initialize all of them from the start.
Seems strange that the servers exhibit such a different behaviour. If there’s a way to make them behave… properly i ‘d be glad to learn about it.