Strange middleman rendering.

config.rb

helpers do
  def icon_tag(icon, copy)
    tag(:i, class: icon) + ' ' + copy
  end
end

test.erb

<ul>
  <li><%= tag(:i, class: 'icon-plus-sign') %></li>
  <li><%= tag(:i, class: 'icon-bar-chart') %></li>
  <li><%= tag(:i, class: 'icon-file') %></li>
</ul>

test.erb.html

<ul>
  <li>
    <i class="icon-plus-sign"></i>
  </li>
  <i class="icon-plus-sign">
    <li>
      <i class="icon-bar-chart"></i>
    </li>
    <i class="icon-bar-chart">
  <li>
    <i class="icon-file"></i>
  </li>
  <i class="icon-file"></i></i></i>
</ul>

test.slim

ul
  li= icon_tag 'icon-plus-sign', 'Calculator'
  li= icon_tag 'icon-bar-chart', 'Formulas'
  li= icon_tag 'icon-file', 'Math words'

test.slim.html

<ul>
  <li><i class="icon-plus-sign"> Calculator</i></li>
  <li><i class="icon-plus-sign"><i class="icon-bar-chart"> Formulas</i></i></li>
  <li><i class="icon-plus-sign"><i class="icon-bar-chart"><i class="icon-file"> Math words</i></i></i></li>
</ul>