Show "last line" rendering problem in Prawn

test-last-line-prawn.rb

#!/usr/bin/env ruby

require 'prawn'
require "prawn/measurement_extensions"

paper_sizes = {
	'A4' => [210, 297],
	'A5' => [148, 210],
	'A6' => [105, 148],

	# XXX: if you uncomment B5, the A6 line will be shown and
	#      the one for B5 will not.
	#'B5' => [176, 250],
}

def arrow_line(pdf)
	bb = pdf.bounds

	v_center = pdf.cursor + 0.8.mm

	#---
	pdf.line [bb.left, v_center], 
	         [bb.right, v_center]
end

pdf = Prawn::Document.new(:page_size => 'A4', :margin => 0)

paper_sizes.to_a.sort.each { |name, size|
	width, height = *size

	format = name.first

	pdf.bounding_box [0, height.mm], :width => width.mm, :height => height.mm do
		pdf.stroke_bounds

		pdf.pad(1.mm) do
			pdf.text name, :align => :right
		end

		arrow_line(pdf)

		pdf.move_up 2.mm
		pdf.text "here should be the line for #{name}"
	end
}

pdf.render_file "test.pdf"