I have two zentyal instances (Both running 5.1).
One is setup as a PDC and the other is setup as a BDC.
If I create a new AD object or DNS entry in the PDC, everything syncs to the BDC just fine.
However, if I create an object in the BDC, it does not sync to the PDC. I am not quite sure what logs to look into or where to start. Hoping to get some guidance!