Using the same output element twice in Shiny

Example taken from Shiny gallery. I would like to show ex1 and ex2 on the first tab, with some breaks between and ex2 on the second tab.

ui.R

navbarPage(
  title = 'DataTable Options',
  tabPanel('Display length',     DT::dataTableOutput('ex1')),
  tabPanel('Length menu',        DT::dataTableOutput('ex2'))
)

server.R

function(input, output) {

  # display 10 rows initially
  output$ex1 <- DT::renderDataTable(
    DT::datatable(iris, options = list(pageLength = 25))
  )

  # -1 means no pagination; the 2nd element contains menu labels
  output$ex2 <- DT::renderDataTable(
    DT::datatable(
      iris, options = list(
        lengthMenu = list(c(5, 15, -1), c('5', '15', 'All')),
        pageLength = 15
      )
    )
  )

}

I thought the following code would work, but it does not. It does show anything in any of the tabs.

navbarPage(
  title = 'DataTable Options',
  tabPanel('Display length',     DT::dataTableOutput('ex1'),
           HTML("<br><br><br>"),
           DT::dataTableOutput('ex2')),
  tabPanel('Length menu',        DT::dataTableOutput('ex2'))
)