Apparently the -XX:+UseNewHashFunction HotSpot option somtimes causes lines to be dropped by Log4J.

Config is basically:
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/" debug="false">
    <appender name="ALL" class="org.apache.log4j.RollingFileAppender">
        <errorHandler class="org.apache.log4j.helpers.OnlyOnceErrorHandler" />
        <param name="File" value="/home/app/log/server.log" />
        <param name="Append" value="true" />
        <param name="MaxFileSize" value="2MB" />
        <param name="MaxBackupIndex" value="100" />
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%d %X{hostname} [%t] %X{jms-type} %X{principal} %-5p %c - %m%n" />
        </layout>
    </appender>

    <root>
        <priority value="debug" />
        <appender-ref ref="ALL" />
    </root>
</log4j:configuration>


see http://java.sun.com/javase/technologies/hotspot/vmoptions.jsp
see API Doc (in src of) HashMap#useNewHash