Not sure if anyone else has run into this issue. but I have a login page with both voucher authentication as well as the standard username/password authentication. I use radius for my user/pass authentication, when is set to re-authenticate the user at regular intervals.
Here is what I run into, when a user is logged in via a voucher. They get bumped off by the radius reauthentication for some reason, even though the voucher system has nothing to do with it. It's not a big deal, as re-authentication is not a big need right now, I can simply turn it off, and things work ok.
but it may be somthing I or somebody might need in the future, so I thought I would share what I has found.
This is similar to the MAC pass through settings. When you use MAC pass through, you get an "unauthenticated" user show up in the list and every minute, m0n0wall will boot it.
The fix for that was to create a username in the Radius for "unauthenticated" with no password and the problem was solved.
This might be a similar issue, when you login with a voucher, check to see what username shows up in the captive portal list. I think they may all be the same, just create a username like that in your radius server so when it verifies the username it won't bump it out.