Thank you for bringing our attention to this issue.
I can confirm that currently there is an issue with the visual state of RadButton
when it is the default form button. I logged the issue is in our issue tracking system and it will be addressed in one of our upcoming releases. Due to the nature of the issue I am not able to provide a work around which solves the issue. I updated your Telerik points accordingly.
Should you have any further questions, do not hesitate to ask.
the Telerik team