modparam("outbound", "force_outbound_flag", 1) doesn't work.

In modules/outbound/ob_mod.c:

int use_outbound(struct sip_msg *msg)
...
/* If Outbound is forced return success without any further checks */
if (ob_force_flag != -1 && isflagset(msg, ob_force_flag) > 0)

isflagset(msg, ob_force_flag) > 0 is always false, it seems the flag is never set.

If I remove isflagset(msg, ob_force_flag) > 0, it works, and the token is added in Path header.

What's the isflagset() supposed to check ?

I'm using the edge proxy example at http://kamailio.org/docs/modules/4.2.x/modules/outbound.html#idp190984

Thanks.