Some logs are generated before loading i3-log.conf. If you want to disable all logs completely, you have to either configure the logging of the Web server[66], or specify log-level when configuring DHtmlLayoutServlet in WEB-INF/web.xml. Refer to the Developer's Reference for details.
<servlet>
<servlet-name>zkLoader</servlet-name>
<servlet-class>org.zkoss.zk.ui.http.DHtmlLayoutServlet</servlet-class>
<init-param>
<param-name>log-level</param-name>
<param-value>OFF</param-value>
</init-param>
...
[66] Remember ZK uses the standard logging utilities. Unless you specify something in i3-log.conf, and the default logging levels depend on the Web server (usually INFO).