stickysession not working with httpd-2.4.6 / mod_cluster-1.2.5.Final

Setup: HTTPD configured as reverse proxy / load balancer for two instances of JBOSS-AS-7.2.0.Final running in HA configuration on two separate nodes.

Consider the following configuration (defined inside my virtual hosts)

<Proxy balancer://mycluster>
ProxySet stickysession=JSESSIONID|jsessionid
</Proxy>

On httpd-2.2.24 / mod_cluster-1.2.0.Final it shows the following behaviour:

• 'stickysession' is working as expected

After upgrading to httpd-2.4.6/mod_cluster-1.2.5.Final things are worse:

• 'stickysession' is ignored and any client request gets dispatched alternatively
  to each one of the two JBoss servers (exactly as if lbmethod=byrequest were defined)

As a final consideration, I read in the docs that stickysession should be enabled by default in mod_cluster anyway, but that is not the case for me.