using cache with json\rest services in wso2esb

using cache with json\rest services in wso2esb

with wso2esb 4.7.0 i deployed the following service to perform a proxy and
expose the same json i get from a different server:
<?xml version="1.0" encoding="UTF-8"?>
<proxy xmlns="http://ws.apache.org/ns/synapse"
name="crmws"
transports="http"
statistics="enable"
trace="enable"
startOnLoad="true">
<target>
<inSequence>
<log level="full"/>
<property name="messageType" value="text/xml" scope="axis2"/>
<cache id="c1"
scope="per-host"
collector="false"
hashGenerator="org.wso2.caching.digest.DOMHASHGenerator"
timeout="6"
maxMessageSize="10000">
<implementation type="memory" maxSize="10000"/>
</cache>
<send>
<endpoint>
<address uri="http://crm/backoffice/webservice.php"
format="rest">
<timeout>
<duration>3000</duration>
<responseAction>fault</responseAction>
</timeout>
</address>
</endpoint>
</send>
</inSequence>
<outSequence>
<log level="full"/>
<property name="messageType" value="application/json"
scope="axis2"/>
<cache id="c1" scope="per-host" collector="true"/>
<send/>
</outSequence>
</target>
<description/>
</proxy>
i then try to implement some cache functionality, but even if first
connection goes well, when i hit cache i get an empty answer with text/xml
content-type.
anyone know where i have to look to fix this issue? regards,