Thank you for writing.
The only reason I can think of that might cause this is if the designer is not properly initialized. Can you please tell me whether the button is showed as component in the tray below the form? If so, than my guess is correct and you can refer to the following article for more information and solution for this case: http://www.telerik.com/support/kb/winforms/details/radcontrols-for-winforms-are-not-loaded-at-design-time
If this is not the case, please let me know how can I replicate the issue you experience and I will do my best to help you resolve it. Please also specify which are the installed versions of the controls you have on your machine and which assemblies (and their versions) are referenced in your project.
I am looking forward to your reply.
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