We just recently switched from Github to Bitbucket. On Github, if I forked one of my team repositories, the permissions for the team were inherited without counting against my individual plan; however, Bitbucket does not work this way and to be honest it really doesn't make any sense. Not only that, but if I manually remove those users from my individual account -- because they're not actually working in my fork -- and then open a pull request from my fork to the main repository, the Team users are prevented from seeing the content of my code in the pull request.
At a very minimum, users of the main repository should be able to see the incoming code in the pull request so that they can approve it. I'm not so concerned about the fact that if they had permissions on the fork repository that it would count against my user count, because no one is actually working in my fork but me. It's a crippling limitation though that they cannot even view the code when a pull request has been submitted. At that point, it makes no sense why the permissions wouldn't be picked up from the original repository instead of the fork since that is where the code is being pulled into.
The suggested proposal of forking into the Team Account instead of my own account doesn't really work for me. I intentionally want a private fork that I can work on a feature in and interactively rebase where I see fit without being concerned about someone else grabbing my branch before it's ready.