I have two modules - the contacts and my own module, which are related with a relationship of one to one.
I create a contact, then create a new record in my own module and assigns it some contact.
If I want to modify any data either from contact or from my own module, I simply enter some record ---> edit ---> modify selected fields ---> save and... on a list of records I see that modified record was duplicated, both of my record from my own module as well as contacts. In both the two records are modified data.
This happens only when the relationship between two modules is one to one!
When I wants to remove any duplicated record of my own module or contacts this will remove the duplication and original record and records from related module.

Why is this happening?

Please help!