dot crashes with assertion failed on graph with some combinations of duplicated edges

When processing some source files with a number of duplicated edges (that is, there exist some nodes A and B such that several edges A->B are declared with various properties), dot fails to produce an output. Usual source files are processed correctly.

Bug exists upstream with detailed steps to reproduce on http://www.graphviz.org/mantisbt/view.php?id=2456 but I could not create an account there (or even login anonymously). This bug report on LaunchPad may be useful to confirm it affects multiple users.

I suspect the reason is duplicated edges because the only Google answer on the assertion failure message is on that Mantis page, and the graphs I was working on do have a number of duplicated edges.

1) The release of Ubuntu you are using, via 'lsb_release -rd' or System -> About Ubuntu

LC_ALL=C lsb_release -rd

Description: Ubuntu 14.10
Release: 14.10

2) The version of the package you are using, via 'apt-cache policy pkgname' or by checking in Software Center

apt-cache policy graphviz

graphviz:
  Installé : 2.38.0-5ubuntu0.1
  Candidat : 2.38.0-5ubuntu0.1
 Table de version :
 *** 2.38.0-5ubuntu0.1 0
        500 http://fr.archive.ubuntu.com/ubuntu/ utopic-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu/ utopic-security/main amd64 Packages
        100 /var/lib/dpkg/status
     2.38.0-5build1 0
        500 http://fr.archive.ubuntu.com/ubuntu/ utopic/main amd64 Packages

3) What you expected to happen

A graphic file is generated.

4) What happened instead

Graphviz stops with message:

dot: class2.c:149: merge_chain: Assertion `(((Agedgeinfo_t*)(((Agobj_t*)(e))->data))->to_virt) == ((void *)0)' failed.

# Additional information

Also observed with graphviz-2.36 on Ubuntu 14.04.

Bug exists upstream with detailed steps to reproduce on http://www.graphviz.org/mantisbt/view.php?id=2456 but I could not create an account there (or even login anonymously). This bug report on LaunchPad may be useful to confirm it affects multiple users.

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: graphviz 2.38.0-5ubuntu0.1
ProcVersionSignature: Ubuntu 3.16.0-31.43-generic 3.16.7-ckt5
Uname: Linux 3.16.0-31-generic x86_64
ApportVersion: 2.14.7-0ubuntu8.2
Architecture: amd64
CurrentDesktop: XFCE
Date: Wed Mar 18 12:04:47 2015
InstallationDate: Installed on 2015-03-04 (13 days ago)
InstallationMedia: Xubuntu 14.10 "Utopic Unicorn" - Release amd64 (20141022.1)
SourcePackage: graphviz
UpgradeStatus: No upgrade log present (probably fresh install)