Directional light in lights.world example causes Ogre assertion in gzclient

[scpeters]

Running the example worlds/lights.world leads to an Ogre assertion in both gazebo9 and gazebo11:

$ gzserver --verbose worlds/lights.world
Gazebo multi-robot simulator, version 9.16.0
Copyright (C) 2012 Open Source Robotics Foundation.
Released under the Apache 2 License.
http://gazebosim.org

[Msg] Waiting for master.
[Msg] Connected to gazebo master @ http://127.0.0.1:11345
[Msg] Publicized address: 192.168.0.197
[Msg] Loading world file [/data_fast/scpeters/ws/gazebo9/src/gazebo/worlds/lights.world]

$ gzclient --verbose
Gazebo multi-robot simulator, version 9.16.0
Copyright (C) 2012 Open Source Robotics Foundation.
Released under the Apache 2 License.
http://gazebosim.org

[Msg] Waiting for master.
[Msg] Connected to gazebo master @ http://127.0.0.1:11345
[Msg] Publicized address: 192.168.0.197
[Err] [InsertModelWidget.cc:426] Missing model.config for model "/home/scpeters/osrf/gazebo_models/.hg"
[Err] [InsertModelWidget.cc:426] Missing model.config for model "/home/scpeters/osrf/gazebo_models/build_mine"
[Err] [InsertModelWidget.cc:426] Missing model.config for model "/home/scpeters/osrf/gazebo_models/joint_limit_twitch"
gzclient: /build/ogre-1.9-B6QkmW/ogre-1.9-1.9.0+dfsg1/OgreMain/include/OgreAxisAlignedBox.h:252:
 void Ogre::AxisAlignedBox::setExtents(const Ogre::Vector3&, const Ogre::Vector3&):
 Assertion `(min.x <= max.x && min.y <= max.y && min.z <= max.z) && "The minimum corner of the box must be less than or equal to maximum corner"' failed.
Aborted (core dumped)

If I comment out the final directional light, then it loads just fine.

[scpeters]

the problem is the <direction>0 0 -1</direction> tag

• https://github.com/osrf/gazebo/blob/gazebo11_11.4.0/worlds/lights.world#L71

changing one of the 0 values to 1e-6 resolves the assertion