Thank you for contacting us.
The issue illustrated in the image attached to your post is a result of the specific settings of the ControlDefault theme. By design, the Default
state of RadButton requires a double border - the outer should be dark blue and the inner should be orange. If we use the standard double border drawing (through setting the BorderBoxStyle property to OuterInnerBorder), the inner border appears with glitches in the corners. In order to avoid the visual issue, in this state the ControlDefault theme assigns an ImageShape, which is rendered as a standard image ignoring the Shape you have applied to the control.
I have logged the aforementioned glitches to our Public Issue Tracker under ID 13399. To vote for it and subscribe for its status updates follow this link: http://www.telerik.com/support/pits.aspx#/public/winforms/13399
. We will do our best to address the rendering issue in a future release, so that the ControlDefault theme design can be achieved without ImageShapes.
Attached is a version of the ControlDefault theme that does not use an ImageShape. It introduces the glitches I have already mentioned if the shape is RoundRectShape with radius 2, however, it allows you to use any custom shape you would like. This is illustrated in the attached sample project. I hope you will find it useful.
Let me know if you have any further questions on this matter.
the Telerik team