Animate inside layout

[Bilal .]

Consider the following code

Shoes.app :width => 200, :height => 200 do
  #flow do
    fill rgb(0xC0, 0xD1, 0xF1, 0.6)
    animate do
      clear do
        rect :left => 50, :top => 50, :width => 100, :height => 100
      end
    end
  #end
end

It does not behave properly when the lines are uncommented. Is the
behaviour expected?
Can anyone explain what's going on behind the scenes when animate
thread runs in a layout.