Hi,
I think that your theory may be correct.
I’ve a site with woocommerce (the last version) and your plugin (last version too) using pagseguro.
It’s strange because, very often, when a visitor clicks on the button to go to pagseguro, he has this error “PagSeguro: Um erro ocorreu ao processar o seu pagamento, por favor, tente novamente ou entre em contato para obter ajuda.” the first time (always the first time) and then if he clicks again on the same button (a second time) it works. That’s why i asked for you about WP Security Plugin.
I have another problem too. I’ve followed your tutorial to install the plugin and the site is using the API only. After the person bought, and waiting a few hours, the status didn’t change (status is waiting : pendente always). There’s nothing in the log specifically. Can I send you the log by e-mail ? I received the email of pagseguro that says the payment has been made?? and approved and can see this payment approved on their site.
Any idea ? Sorry for disturb.