Image.drawMap doesn't render the updated map buffer

[pmgl]

init = function()
  viewport = new Image(100,100,true)
end

update = function()

end

draw = function()
  screen.clear("#222")

  viewport.clear("#371")
  viewport.drawText("TEST",0,45,12,"#fff")
  // screen.drawMap("map1",0,0,240,160)     // this shouldn't be here !!!
  viewport.drawMap("map1",0,0,240,160)    // map doesn't render

  screen.drawImage(viewport,0,0,100,100)
end