Why does killing GS with SIGHUP crash on the 2nd time?

[Marco Scannadinari <marco scannadinari co uk>]

I'm in the process of developing an app in Python (3). One of the
functions it has it the restart the shell. I would like to refrain from
relying on calling commands from the shell using subprocess.call([]),
and so I used:
    os.kill((GS PID), 1) # 1 == SIGHUP

For some reason, using this command twice crashes the shell. It is not
python-specific, as pkill -HUP gnome-shell and killall -HUP gnome-shell
produce the same result, which is odd because Alt+F2 + "r" * (a lot)
does not crash it.

Should I be issuing a different signal to gnome-shell, or do I have to
use gnome-shell --replace from the commandline? 
-- 
Marco Scannadinari <marco scannadinari co uk>