Borders on button using custom layout template

Question

When I use the custom layout template I created using Ribbon.SizeDefinitions, all buttons now have borders. Has anyone else had this problem? How do I get rid of the borders? Here is the XML.

  <!-- ***** Custom Template like ThreeButtonsAndOneCheckBox but with the checkbox on top ***** -->
  <Ribbon.SizeDefinitions>
    <SizeDefinition Name="ThreeButtonsOneCheckBoxOnTop">
      <ControlNameMap>
        <ControlNameDefinition Name="button1" />
        <ControlNameDefinition Name="checkbox1" />
        <ControlNameDefinition Name="button2" />
        <ControlNameDefinition Name="button3" />
      </ControlNameMap>
      <!-- Large Definition -->
      <GroupSizeDefinition Size="Large">
        <Row>
          <ControlGroup>
            <ControlSizeDefinition ControlName="button1" ImageSize="Large" IsLabelVisible="true"/>
          </ControlGroup>
          <ControlGroup>
            <ControlSizeDefinition ControlName="checkbox1" IsLabelVisible="true"  IsImageVisible="false"/>
          </ControlGroup>
          <ControlGroup>
            <ControlSizeDefinition ControlName="button2" ImageSize="Large" IsLabelVisible="true" />
          </ControlGroup>
          <ControlGroup>
            <ControlSizeDefinition ControlName="button3" ImageSize="Large" IsLabelVisible="true" />
          </ControlGroup>
        </Row>
      </GroupSizeDefinition>
      <!-- Medium Definition -->
      <GroupSizeDefinition Size="Medium">
        <ControlGroup>
          <ControlSizeDefinition ControlName="button1" ImageSize="Large" IsLabelVisible="true"/>
        </ControlGroup>
        <!-- Separator Bar -->
        <ColumnBreak ShowSeparator="true"/>
        <Row>
          <ControlGroup>
            <ControlSizeDefinition ControlName="checkbox1" IsLabelVisible="true"  IsImageVisible="false"/>
          </ControlGroup>
        </Row>
        <Row>
          <ControlGroup>
            <ControlSizeDefinition ControlName="button2" ImageSize="Small" IsLabelVisible="true" />
          </ControlGroup>
        </Row>
        <Row>
          <ControlGroup>
            <ControlSizeDefinition ControlName="button3" ImageSize="Small" IsLabelVisible="true" />
          </ControlGroup>
        </Row>
      </GroupSizeDefinition>
      <!-- Small Definition -->
      <GroupSizeDefinition Size="Small">
        <ControlGroup>
          <ControlSizeDefinition ControlName="button1" ImageSize="Large" IsLabelVisible="true"/>
        </ControlGroup>
        <!-- Separator Bar -->
        <ColumnBreak ShowSeparator="true"/>
        <Row>
          <ControlGroup>
            <ControlSizeDefinition ControlName="checkbox1" IsLabelVisible="true"  IsImageVisible="false"/>
          </ControlGroup>
        </Row>
        <Row>
          <ControlGroup>
            <ControlSizeDefinition ControlName="button2" ImageSize="Small" IsLabelVisible="true" />
          </ControlGroup>
        </Row>
        <Row>
          <ControlGroup>
            <ControlSizeDefinition ControlName="button3" ImageSize="Small" IsLabelVisible="true" />
          </ControlGroup>
        </Row>
      </GroupSizeDefinition>
    </SizeDefinition>