Hi Hakan,
in this case this is not an interaction web client role. We are using a customized version of standard role marketingpro.
Implementing a check before or directly after ORDER_SAVE BAdI will not help because the issue is not yet present there and at first happens when this update function module is called. A check would only be helpful directly in this function module to check for already existing entries in db table.
To implement a check in this update function module I would have to do a modifiation, which we don't do in our SAP CRM environment.
When I started researching I looked for issues in our code and didn't find any. Then I started looking for an SAP Note and wasn't successful. After that I created this post because I find it more helpful than creating a ticket to SAP.
Now I will raise a ticket to SAP explaining the situation and ask for a solution.
Thank you for all your effort :-)
Best regards
Sascha