Hi Stefan,
Thank you for posting your query to us.
I am afraid that i am not able to reproduce the issue. I have attached the sample under which i tried to reproduce the issue and it is available here.
http://www.syncfusion.com/Support/user/uploads/Merge_671cfcfe.zipPlease sent us the sample along with the input documents or modify the above sample so that it will be helpful for us to reproduce the issue here.
Regards,
Sarathi