Model_id and branch_id are null in IAM sync file

I am investigating a slow IAM sync and stumbled upon the problem below. We sync our IAM by first syncing to disk and then use the twdeployer to sync the target IAM. 

1. I sync a branch to disk with the task in the SF.
2. I open the file MODEL_SYNC.sql and copy the varbinary of sync_col for example
3. I convert the varbinary with convert(xml, decompress( sync_data)) to take a look at the xml
4. If i look at the xml there no nodes for model_id and branch_id in the XML (which could be logical as the sync file has been generated for a specific model and branch)
5. However the procedure sync_col on the IAM databse expects model_id and branch_id in the XML. In the temp table model_id and branch_id are now NULL because they are not in the XML.

   

6. And then in the merge

   

7. So as no match can be made because model_id and branch_id are NULL all rows are inserted from the temp table and all the old rows are deleted.

Is the above correct? Or am i missing a setting that causes the model_id and branch_id not be included in the XML.