title: how to feed two uiOutput to renderUI within tabs
body: <p>When I try to feed to <code>uiOutput</code> to <code>renderUI</code> while using <code>tabPanel</code> in shiny I get an error in the first run. After switching tabs, the app runs ok. </p>
  
  <p>Here is a minimal example that reproduces the error</p>
  
  <pre><code>library(shiny)
  ui &lt;- fluidPage(
      tabsetPanel(
          tabPanel("Data", 
                   uiOutput("moreControls") 
          ),
          tabPanel("Research",
                   uiOutput("moreControls2") 
          )
      ),
      plotOutput("plot1")
  )
  
  server &lt;- function(input, output) {
      output$moreControls &lt;- renderUI({
          tagList(
              sliderInput("mean", "Mean", -10, 10, 1),
              textInput("label", "Label")
          )
      })
  
      output$moreControls2 &lt;- renderUI({
          tagList(
              sliderInput("sd", "SD", 1, 50, 10),
              textInput("label2", "Label2")
          )
      })
  
      output$plot1 &lt;- renderPlot({      
          hist(rnorm(n = 100,input$mean, input$sd) , xlim = c(-100, 100) )
      })
  
  }
  shinyApp(ui, server)
  </code></pre>