Indeed, I managed to reproduce the issue you reported on our demos. I will investigate it and let you know once I could provide more information on the topic.
In the meantime, I tested the case by extracting RadCalculator's template with Expression Blend and defining additional row with the corresponding buttons for the custom commands and everything works as expected. Could you try this approach without copying directly the template from our demos ? Do you get the same behavior ?
the Telerik team