Not able to fetch ${catalina.base}, system property not working in log4j2.xml?

Question

Previously we had a log4j 1.x compatible xml format which was having this Rolling file appender configured-

<appender name="ALL" class="org.apache.log4j.RollingFileAppender">
        <param name="File" value="${catalina.base}/logs/trw.log" />
        <param name="Append" value="true" />
        <param name="MaxFileSize" value="4096KB" />
        <param name="MaxBackupIndex" value="10" />
        <layout class="org.apache.log4j.PatternLayout">
            <param name="ConversionPattern" value="%d %p [%t] %C{1}:%L - %m%n" />
        </layout>
    </appender>

Now I have changed it to the new log4j2.xml format where based on my research the catalina.base becomes like so -

    <RollingFile name="ALL" fileName="${sys:catalina.base}/logs/trw.log"
                     filePattern="${sys:catalina.base}/logs/trw_%i.log"
                     append ="true">
            <PatternLayout pattern="%d %p [%t] %c{1}:%L - %m%n"/>
            <Policies>
                <SizeBasedTriggeringPolicy size="4096KB" />
            </Policies>
            <DefaultRolloverStrategy max="10"/>
        </RollingFile>

But when I run a test file which uses this logging configuration, the xml file is found and loaded and all is going well but instead of finding the system variable cataline.base it creates a folder ${sys:catalina.base} and puts the log under it. My question is that - is this the expected behaviour ? Does log4j2.xml config try to search for the system property and if not found just creates a folder with that name ? This config is in a web-application which runs on TomCat 7, spring 3.1 and servlet 2.5. Logs are getting generated as expected but only folder name seems to be the issue.