title: plotly giving incorrect text on hover in stacked bar charts
body: <p>I'm using <code>plotly</code> with RStudio.</p>
  
  <p><code>plotly</code> is giving incorrect text on hover for stacked bars in the chart except for the top most bar.</p>
  
  <p><strong>Reproducible example</strong></p>
  
  <pre><code>  df &lt;- data.frame(
      make = rep(c('Toyota', 'Honda', 'Volkswagen'),4),
      segment =c(rep('high',3), rep('mid',3), rep('low',3), rep('entry',3) ),
      sales=c( 25,35,75, 35,35,30, 45,25,10, 80, 80, 20)
    )
  
  df
           make segment sales
  1      Toyota    high    25
  2       Honda    high    35
  3  Volkswagen    high    75
  4      Toyota     mid    35
  5       Honda     mid    35
  6  Volkswagen     mid    30
  7      Toyota     low    45
  8       Honda     low    25
  9  Volkswagen     low    10
  10     Toyota   entry    80
  11      Honda   entry    80
  12 Volkswagen   entry    20
  
    p &lt;- ggplot(df, aes(x=make, y=sales) ) +
      geom_bar(stat="identity", aes(fill=segment), position = "stack")
    ggplotly(p)
  </code></pre>
  
  <p>What I get in RStudio is as in the pictures below. As you would see except for the top stacked bar, everything else is giving the wrong text on hover </p>
  
  <p><strong>Incorrect text on hover</strong> - based on data in <code>df</code> the correct value for <code>sales</code> is <code>20</code> - instead it is showing <code>135</code> - data - <code>12 Volkswagen   entry    20</code>
  <a href="https://i.stack.imgur.com/KsR9u.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/KsR9u.jpg" alt="enter image description here"></a></p>
  
  <p><strong>Correct text on hover</strong> - only observed for the top most bar in stack.
  <a href="https://i.stack.imgur.com/IzjjZ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/IzjjZ.jpg" alt="enter image description here"></a></p>
  
  <pre><code>&gt; packageVersion('ggplot2')
  [1] ‘2.2.1’
  &gt; packageVersion('plotly')
  [1] ‘4.5.6’
  &gt; 
  </code></pre>