Transport stack default value always set to `tcp`

The default transport configuration in the server is the following:

   <cache-container name="default" statistics="true">
      <transport cluster="${infinispan.cluster.name}" stack="${infinispan.cluster.stack:tcp}" node-name="${infinispan.node.name:}"/>
   </cache-container>

If the xml is updated so that {{ stack="${infinispan.cluster.stack:udp}" }} and the property is not set on launch, the "tcp" stack is still loaded instead of "udp".

Conversely, simply specifying stack="udp" works as expected, with the "udp" stack loaded.