When connecting to a server that sets topology subnet, tun interface should be setup as BROADCAST. The added patch was also sent to openvpn bug tracker, on ticket #425.
This is under discussion by the OpenVPN upstream maintainers, so see if you can get away with an --up script or thereabouts for now. I'll wait for the outcome of the upstream discussion.
rejected per cron2's comment in upstream BTS
Is this discussion public? Do you have any URL if it is? Regards
upstream reopened the bug, so do we.
Renato, the discussion so far takes place in the upstream tracker, URL is listed above in "See Also", and in Comment 2.
Renato reported the issue fixed in the upstream bug and asked to close it, so we'll close this downstream bug, too. Apparently the routing issue is specific to pfSense.