Thanks for contacting us and for the provided screenshot.
I have investigated the issue you reported and was able to reproduce it. This is an undesired behavior and we are going to research it.
In the meantime, I would suggest you create your form with a RadRibbonBar by inheriting from the ShapedForm class. You can add the rounded corners to this form by setting the Shape property of the form to RoundRectShape so that it looks like the RibbonForm.
I hope this will help you achieve the desired appearance. Please, write back if you have further questions or need assistance.
the Telerik team
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