Option "-z" does not work when X not configured

Somehow similar to bug #165983, but not completely. We are running inkscape on a server without X for converting SVG images. In principle, inkscape offers a nice batch mode via the "-z" option, but this seems not to be implemented consistently. If you run inkscape as a normal user your get

Xlib: connection to "localhost:11.0" refused by server
Xlib: PuTTY X11 proxy: MIT-MAGIC-COOKIE-1 data did not match
(inkscape:24050): Gdk-CRITICAL **: gdk_display_list_devices: assertion `GDK_IS_DISPLAY (display)' failed
301.27942

so despite some error messages you get the expected output. If you do the same as apache user (which doesn't have the X authorization files) you get

$ inkscape -z -W drawing.svg
X11 connection rejected because of wrong authentication.
The application 'inkscape' lost its connection to the display localhost:11.0;
most likely the X server was shut down or you killed/destroyed
the application.

so inkscape does not run properly.

It would be nice to be able to run inkscape without any need for X at all.