One of the possible reasons for this layout of the text is that there is a section break of type Continuous in the docx document. This is a valid option according to the Open XML specification, but is not supported by RadRichTextBox. For a list of supported section-break types you can refer to this article.
If this is not the case with your document, the difference in the layout may be due to some other unsupported feature or a bug. As the specification is rather vast and our clients usually have a wider document reach, we have adopted the habit of looking into import issues once a sample document is submitted through the support ticketing system. Therefore, if you would like us to further investigate the problem, please open a support ticket and attach a document illustrating the issue.
All the best,
the Telerik team