This looks to me like an issue with bad behavior script that some sites use
to prevent spammers. http://bad-behavior.ioerror.us/support/faq/ shows some
suggestions.
It has been a long time since I've worked with bad behavior. If I remember
correctly, Bad Behavior does not block bad IPs per se, but instead blocks bad
configurations, as spammers are not that good at configuring well. (For
example, malformed User Agents).
This leads me to believe (unless I'm wrong, of course), that bad behavior
does not block the VPN IP but whatever config you have that is wrong, which
is what you should check into. What other configurations do you have when you
use the VPN than when you are not?
I also believe that badbehavior keeps a log of errors, if any webmaster on
trisquel's forums has access to the log and can lookup the issue you're
having they might be able to point you in the right direction.
Welcome to the world of preventing spam :/. It's always a balancing act of
trying to prevent spammers and not users, clearly it doesn't work perfectly.
