To reproduce:
1. Open the Demo application >> RichTextBox >> First look example
2. Clear the whole existing content
3. Enter "aaa" and press enter
4. Press enter to insert an empty paragraph
5. Enter "bbb"
6.Select the whole content and press the ordered list button
7. Save the content as HTML
8. Load the exported file

You will noticed that you have two separate ordered lists

Resolution: 
This issue is addressed in the new version of the control - RadRichTextEditor. Please use the new control instead the RadRichTextBox.