mogrify draw rectangle produces distorted borders

[universa1]

Drawing a rectangle using mogrify produces distorted borders. I used for example the following command:

mogrify -draw 'stroke red stroke-width 5 fill red fill-opacity 0.1 rectangle 100,100 150,150' c1.png

This results in distorted borders, but correct background rectangle. See the attached image. The bug also happens when using rmagick. The bug also happend both on Ubuntu 13.10 and 14.04. I upgrade to 14.04 to see if that fixes the problem, but it didn't. Drawing a circle works fine.

lsb_release -rd
Description: Ubuntu 14.04.1 LTS
Release: 14.04

apt-cache policy imagemagick
imagemagick:
  Installiert: 8:6.7.7.10-6ubuntu3
  Installationskandidat: 8:6.7.7.10-6ubuntu3
  Versionstabelle:
 *** 8:6.7.7.10-6ubuntu3 0
        500 http://de.archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
        100 /var/lib/dpkg/status

[broucaries (roucaries-bastien+bugs)]

http://www.imagemagick.org/discourse-server/viewtopic.php?f=3&t=27557