Strange treeview behaviour: strikeout text only if bold

I need to show some treeview item text striked out text into a QT treeview from Ruby. After some reading on QT documentation and much coding, I found that only when rendering font in bold, also the strikeout was rendered.

So I wonder, where I'm doing wrong? This is the code to achive the result shown above. Note as I set strikeout for every even row item. I'm using Ruby 1.8.7 and Qt 4.6.2 and qt4ruby 4.4.3-6 on Mandriva Linux.

require 'Qt4'
require 'date'

class MyStandardItem < Qt::StandardItem     
  def initialize(str = nil)
    super str
  end

  def data(role = Qt::UserRole + 1)
    return super(role) unless role == Qt::FontRole
    ret_val = Qt::Font.new()
    #parameters for "fromString":font family, pointSizeF, pixelSize, QFont::StyleHint, QFont::Weight, QFont::Style, underline, strikeOut, fixedPitch, rawMode
    ret_val.fromString "sans serif,-1,-1,0,0,0,0,0,0,0"
    case role
    when Qt::FontRole
      ret_val.setStrikeOut(true) if (index.row % 2) == 0
      if index.column == 1
    ret_val.weight = Qt::Font.Bold
      else
    ret_val.weight = Qt::Font.Normal
      end
      return Qt::Variant.fromValue(ret_val)
    end
    return ret_val
  end  
end

Qt::Application.new(ARGV) do
  treeview = Qt::TreeView.new do
    model = Qt::StandardItemModel.new self
    head = [MyStandardItem.new "Qt v. #{Qt.version}"]
    head << MyStandardItem.new("Ruby v. #{开发者_运维技巧VERSION}")
    head << MyStandardItem.new("Qt4Ruby v. 4.4.3-6 (Mandriva)")
    model.append_row head
    (1..10).each do |i|
      col0 = MyStandardItem.new 'some text'
      col0.check_state = ((i % 3) == 0)? Qt.Checked : Qt.Unchecked
      col0.checkable = true
      col0.editable= false
      col1 = MyStandardItem.new "line ##{i}"
      col2 = MyStandardItem.new((Date.today + i).strftime '%d/%m/%y')
      model.append_row [col0, col1, col2]
    end
    self.model = model
    show
  end
  exec
end

Eventually I find an hackish trick to overcome this problem. Playing around after reading again the enum QFont::Weight description I tried to set

ret_val.weight = 51 # Qt::Font.Normal value is 50

instead of

ret_val.weight = Qt::Font.Normal

and magically the normal text appears striked out!

Maybe this strange behaviour is due to a bug on QT?