I don't know if this is a bug or I am doing something wrong but when
loading sac files with obspy read command header fields dist, az, baz and
gcarc are not set. If I read sac file "test.sac" in which those header
fields are set (or calculated) with SAC everything is fine.
For example:
I can't reproduce your problems. If I go to directory
"obspy/sac/tests/data" and read the file "test.sac" with SAC I get no
header values contrary to your report:
SEISMIC ANALYSIS CODE [06/12/2013 (Version 101.6)]
Copyright 1995 Regents of the University of California