Missing line when scaling 0.5 and setting stroke-antialias 0

[donv]

Hi!

Using rmagick (2.13.2) with ImageMagick 6.8.6 on OS X 10.8.4. Given the following example:

script = <<EOF
scale 0.5,0.5
stroke-antialias 0
line 63.2031,377.2 780,377.2
line 63.2031,335 780,335
line 63.2031,292.8 780,292.8
EOF
require 'rmagick'
d = Magick::Draw.new
script.each_line { |line| d.primitive line }
base_image = Magick::Image.new(400, 300)
d.draw(base_image)
base_image.write('three_lines.png')

I get the following image:

I expect three lines to be drawn, but there are only two. Any idea why?

Any help is appreciated.