1. Run Blender
2. Change Audio backend to "Jack" (should be "JACK" - all letters uppercase, because it's an acronym, but nevermind).
3. Enable Audio/Video sync using the Sync Mode combobox on the Timeline header.
4. Run Ardour (or another program that uses JACK transport)
5. Move the playhead in BLender to make sure that the playhead in Ardour follows along.
6. Press play in Ardour
7. Watch Blender segfault.
I did a quick test it and the crash doesn't occur in Blender 2.76b - all works fine there.