Everybody that has finished and mastered the first level in brazil will be experiencing this problem until Zynga get's off their butts and fixes it, which is something they should've done before they released it!
And since there are items involved, that are awarded upon completion of the mission in addition to the mastery rewards.. you might wanna hold off on Brazil until this is fixed! Otherwise, there's gonna have to be a lot of unnecessary communication between you and zynga to get what you deserve... and nobody wants that!
Ah, Brazil.. More like AHH!! Brazil...
I already sent them this email about this issue (Since their live chat is NEVER up): I'm stuck on the first mission because i have already mastered the first level of Brazil.. so I can't continue on with the event. Once again this is a huge Inconvience. This happened with the Italy missions too. Ya figure you would have worked this out by now especially since the exact same problem has happened before.
I'm sure a lot of people are slamming their inbox with the same sort of thing.. I'm not telling you to do the same thing, that will probably cause more problems than it would solve, but let them hear it if you wanna.. They really need to start testing things before they release it!