title: conditionalPanel doesn't update when changing the condition
body: <p>I am trying to build a shiny app. in my code, I use a conditional panel as the following, where the user choose between different <code>input.pkmodel</code>, and based on that different set of parameters appear to the user</p>
  
  <pre><code>library("shiny")
  ui &lt;- fluidPage(theme = shinytheme("united"),        
  actionButton("go", "RUN"),
  
  selectInput("PKmodel",
          "Select the PK Model:",
          choices = list(" 1 Compartment Model" = 1,
                         " 2 Compartment Model" = 2),
  
          selected = 1),
  conditionalPanel(
  condition = "input.PKmodel == 1",
  numericInput("CL", "CL:", 5, min = 0.000001, max = 10000,step = .01)
  ),
  conditionalPanel(
  condition = "input.PKmodel == 2",
  numericInput("CL", "CL:", 20, min = 0.000001, max = 10000,step = .01),
  numericInput("VC", "V:", 13, min = 0.0000001, max = 20,step = .01))
  )
  
  
  
  server &lt;- function(input, output) {
  
  sim.data &lt;- eventReactive(input$go,{
  selectPKmod &lt;- input$PKmodel 
  if (selectPKmod == 1) {
    CLIN&lt;-input$CL    }
  if (selectPKmod == 2) {
    CLIN&lt;-input$CL 
    VCIN&lt;- input$VC }
  } )
  }
  shinyApp(ui = ui, server = server)
  </code></pre>
  
  <p>I am facing this issue:
  When I select input.PKmodel == 2 , the CL parameter value doesn't change neither to 20 "the default for input.PKmodel == 2" nor to any user defined value. But instead it stays as CLIN=5  "the default for input.PKmodel == 1" .</p>
  
  <p>In other words, If I select input.PKmodel == 2, then changed  the value of either VCIN or CLIN "using the user interface", neither of these values do change.
  For CLIN it stays fixated to the value of 5 (from default value input.PKmodel == 1),
  and the VCIN parameter stays fixated to the value of 13 (from input.PKmodel == 2). So it seems that the parameters get the value of the first time they appear, but they dont get updated.
  Could you please help solve this issue? also , please notice that I am using actionButton and eventReactive  ( I am not sure if this has a relation to the issue).
  Thanks </p>