Why Spring batch executing as singleton instead of multithread

I am invoking a spring batch job through quartz scheduler, which should run every 1 minute. When the job runs the first time, the ItemReader is opened successfully and the job runs. However when the job attempts to run a second time, it's using the same instance it did the first time which is already initialized and receiving "java.lang.IllegalStateException: Stream is already initialized. Close before re-opening." I have set scope as step for both itemreader and itemwriter.

Please let me know if I am doing anything wrong in configuration?

<?xml version="1.0" encoding="UTF-8"?>

<import resource="context.xml"/>
<import resource="database.xml"/>   
<bean id="MyPartitioner" class="com.MyPartitioner" />
<bean id="itemProcessor" class="com.MyProcessor" scope="step" />

<bean id="itemReader" class="com.MyItemReader" scope="step">
    <property name="dataSource" ref="dataSource"/>
    <property name="sql" value="query...."/>
    <property name="rowMapper">
        <bean class="com.MyRowMapper" scope="step"/>
    </property>
</bean>

<job id="MyJOB" xmlns="http://ift.tt/1fayA4Z">
    <step id="masterStep">
        <partition step="slave" partitioner="MyPartitioner">
            <handler grid-size="10" task-executor="taskExecutor"/>
        </partition>
    </step>
</job>
<step id="slave" xmlns="http://ift.tt/1fayA4Z">
    <tasklet>
        <chunk reader="itemReader" writer="mysqlItemWriter" processor="itemProcessor" commit-interval="100"/>
    </tasklet>
</step>

<bean id="taskExecutor" class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor">
    <property name="corePoolSize" value="20"/>
    <property name="maxPoolSize" value="20"/>
    <property name="allowCoreThreadTimeOut" value="true"/>
</bean>

<bean id="mysqlItemWriter" class="com.MyItemWriter" scope="step">
    <property name="dataSource" ref="dataSource"/>
    <property name="sql">
        <value>
            <![CDATA[      
            query.....
        ]]>
        </value>
    </property>

<property name="itemPreparedStatementSetter">
        <bean class="com.MyPreparedStatementSetter" scope="step"/>
    </property>
</bean>