Trouble with overriding properties in Spring-batch - spring

Question

We are using Spring 4.3.9 with Spring Batch 3. We are using maven to copy resources with filtering to merge profile-based properties into the configs at build time. I want to allow my DevOps engineers to override property file settings (db passwords) at deployment time to the environment specific property, so I've setup things as shown below, but the overrides don't work:
<bean class="org.springframework.beans.factory.config.PropertyOverrideConfigurer">
<property name="location" value="classpath:bluecost-OVERRIDE.properties" />
</bean>
<bean id="dataSource"
class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close">
<property name="driverClass" value="${datasource.database.driverClassName}" />
<property name="jdbcUrl" value="${datasource.database.url}" />
<property name="user" value="${datasource.database.username}" />
<property name="password" value="${datasource.database.password}" />
<property name="maxPoolSize" value="${datasource.maxPoolSize}" />
<property name="minPoolSize" value="${datasource.minPoolSize}" />
</bean>
The property file that maven merges with all default values looks like this:
datasource.database.driverClassName=com.ibm.db2.jcc.DB2Driver
datasource.database.url=jdbc:db2://localhost:50000/bluecost
datasource.database.username=not-real-id
datasource.database.password=not-real-pwd
datasource.maxPoolSize=50
datasource.minPoolSize=10
And finally, my bluecost-OVERRIDE.properties file has the correct values for just the username and password, configured like this:
# Overriding values for the datasource property values
datasource.database.username=db2inst
datasource.database.password=db2inst1
The override file is surely in the classpath (it wouldn't start without finding it anyway). It's throwing errors at runtime because of the invalid (default) userid/pwd.
Why doesn't it override the userid/pwd like I want it to?