If you set up your server so that the web interfacebase URL is:
http://server/sympa
And you find URL cropped to:
http://server/lists http://server/list/sendpasswd/ etc.
instead of:
http://server/sympa/lists http://server/list/sympa/sendpasswd/ etc.
It is likely that the env_reset option of sudo was set. This option removes all environment variables, including those sent to Sympa by the web server, which indicate the base URL for all the links in the web interface.
See sudo to set up the correct sudo configuration.