RollingRandomAccessFile appender loses output when fileName/filePattern accesses ${sys:property}

    <RollingRandomAccessFile name="RollingRandomAccessFile" 
        fileName="logs/${sys:Fubar}.log"
        filePattern="logs/$${date:yyyy-MM-dd}/${sys:Fubar}-%d{MM-dd-yyyy}-%i.log.gz">

    public static void main(String[] args) {
        for (int i=0; i < 100000; i++) {
            logger.info("Logger writes message for the nth time " + i);
        }
        System.out.println("Done");
    }