Deferred UI breaks Shiny app

app.R

# example Shiny app where uiOutput is only rendered when panel is selected, but other
# items are dependent on the deferred UI.

library(shiny)

ui <- fluidPage(
    tabsetPanel(tabPanel("Main", 
                         plotOutput("dots")),
                tabPanel("Settings",
#                         checkboxInput('even','Even?',TRUE)
                         uiOutput("even.or.odd")
                )
    )   
)

server <- function(input, output) {
   
   output$dots <- renderPlot({
     plot(seq(ifelse(input$even, 0, 1), 20, 2))
   })
   output$even.or.odd <- renderUI(checkboxInput('even', "Even?",TRUE))
}

shinyApp(ui = ui, server = server)