Connection is lost when putting the handler in session

I've made a script that use ezcSearchSolr, I can create the search sessionand do request.

$this->session = new ezcSearchSession(
new ezcSearchSolrHandler($domain, $port , $uri."/".$location),
new ezcSearchEmbeddedManager()
);

When I put this search session inside the PHP session, I can do the first request and after that the $this->session->handler->connection is null.
If you reinit the session at each time, it will work.