hmm, I set up a fresh config like this with 1.0.1 and it worked fine. Do all NAT entries stop working or is it something more specific? What version of pfsense? Normal behavior of the captive portal is to block outgoing access until credentials can be verified. All hosts, unless specified in the passthrough, will not be able to reach the WAN until said credentials are provided and verified. Do you get redirected to the portal page at all?
After you enable the captive portal log in and type
pfctl -s nat|grep -v 127.0.0.1
as well as
ipfw list
and post the results.