**System Information**
Archlinux
**Blender Version**
Broken: 2.73
**Short description of error**
Smoke simulations gives strange results when using multiple parented collision objects.
**Exact steps for others to reproduce the error**
1. Open {F145317}
2. Play animation or bake the smoke simulation
3. Observe strange results
4. Join the grouped collision objects
5. re-bake the simulation
6. Simulation now works as expected