Hi
Thanks for your reporting this issue to us. I have reproduced this problem and logged it to our defect base as issue # 3658. We will try to fix it in one of future releases. The notification will be posted here in this thread as soon as it will be done.
Best regards.
The issues you have found earlier (filed as 3658) have been fixed in this update.
Issue #3658 - “Cannot add a style because a style with the same name already exists” exception occurs during inserting one document into another.
The problem occurs when destination document contains a user defined style with a name of a built in style.