that does look odd, but unfortunatly I haven't been able to replicate this. Here's a couple of ideas though.
- If your using inerited controls, then have a look at this
which explains ensuring that you will pick up the theme class name
- Check to make sure that all the Telerik assemblies that you are referencing are the latest ones, and not one from an old installation.
- Try this in a new project. Just adding the RadRibbonForm.
If none of these help, then if you could provide the code here to replicate it, I'll be happy to take a look