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>

Error stack trace -

org.springframework.batch.item.ItemStreamException: Failed to initialize the reader
        at org.springframework.batch.item.support.AbstractItemCountingItemStreamItemReader.open(AbstractItemCountingItemStreamItemReader.java:142)
        at sun.reflect.GeneratedMethodAccessor294.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:601)
        at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
        at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:131)
        at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:119)
        at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
        at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
        at com.sun.proxy.$Proxy165.open(Unknown Source)
        at org.springframework.batch.item.support.CompositeItemStream.open(CompositeItemStream.java:96)
        at org.springframework.batch.core.step.tasklet.TaskletStep.open(TaskletStep.java:306)
        at org.springframework.batch.core.step.AbstractStep.execute(AbstractStep.java:192)
        at org.springframework.batch.core.partition.support.TaskExecutorPartitionHandler$1.call(TaskExecutorPartitionHandler.java:139)
        at org.springframework.batch.core.partition.support.TaskExecutorPartitionHandler$1.call(TaskExecutorPartitionHandler.java:136)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
        at java.util.concurrent.FutureTask.run(FutureTask.java:166)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
        at java.lang.Thread.run(Thread.java:722)
Caused By: java.lang.IllegalStateException: Stream is already initialized.  Close before re-opening.
        at org.springframework.util.Assert.state(Assert.java:384)
        at org.springframework.batch.item.database.AbstractCursorItemReader.doOpen(AbstractCursorItemReader.java:399)
        at org.springframework.batch.item.support.AbstractItemCountingItemStreamItemReader.open(AbstractItemCountingItemStreamItemReader.java:139)
        at sun.reflect.GeneratedMethodAccessor294.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:601)