Hi Timo!
A couple of years ago you reported a bug against the xplanet package in
Debian, and I just stumbled over that bug report.
I tried to reproduce it with the xplanet package 1.3.0-5.1 - the version
which is currently shipped in Debians stable release, but unfortunatly I
was unable to reproduce it.
Using
https://upload.wikimedia.org/wikipedia/commons/e/e9/Location_map_Japan.png
as a replacement for your japan.png and running the exakt command you
gave with the configuration and markers file you provided with the bug
report, I got a readable output.
Could you please retry it, and if you still have a problem provide an
example of the result? By now the link you provided in your original
report doesn't work anymore :(
Best regards,
Alexander