I would think that region defines how you want the displays to behave, not where you actually are. GPS will let the device know where it is and what is local. I wouldn't expect to change my settings if I went abroad. Mine are set for UK and English respectively and dates show in dd/mm/yyyy format in Mail for example.
Presumably setting to Brazil & English gives US style dates, rather than UK ones, though I cannot see why. It should be easy enough to pick the correct mode: http://en.wikipedia.org/wiki/Date_format_by_country. Perhaps it is a bug.
tt2