if 'DPKG_RUNNING_VERSION' in os.environ and options.signal:
# This is what happens when we are called in an obsolete postinst/prerm script
# Do nothing, it will be done in the trigger
sys.exit(0)
So when the postinst script calls update-gconf-defaults it just exits.
Looking at update- gconf-defaults we see:
if 'DPKG_RUNNING_ VERSION' in os.environ and options.signal:
# This is what happens when we are called in an obsolete postinst/prerm script
# Do nothing, it will be done in the trigger
sys.exit(0)
So when the postinst script calls update- gconf-defaults it just exits.