Dropdown menus can not be opened in tc:sheet header

<tc:column label="Name">
  <f:facet name="bar">
    <tc:button label="Dropdown" omit="true">
      <tc:link label="Entry"/>
      <tc:link label="Entry"/>
    </tc:button>
  </f:facet>
  <tc:out value="#{object.name}"/>
</tc:column>