Portuguese style guideline (https://musicbrainz.org/doc/Style/Language/Portuguese) isn't clear enough about the capitalization of the first word after opening bracket (part of title / not extra title information).

Also says:
Pode-se conseguir a aplicação dessas regras ativando a opção "Sentence Mode" e Guess Case.

Translating: You could get this rules applied activating the 'Sentence Mode' option and 'Guess Case'.

"Sentence Mode" at now capitalizes this first word.