Thank you for reporting this issue.
This is a regression one and I am reopening the case.
I am not able to provide a workaround through Visual Style Builder because this theme uses images to draw the Checkmark and this image is missing for the disabled state. As a workaround, I can suggest to set the enabled state to true (if false) and then set the Cheked property:
radCheckBox.Checked = isChecked;
Please refer to the attached sample project that demonstrates this approach. I hope this helps.
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