I teach ESL students who are nearly fluent in English after years of study and they STILL make small errors with articles and spelling. I think for a beginning course, minor errors should be marked as correct. It's how we learn-- Once again I was "docked" because I forgot one letter! I left out ONE letter and my answer was marked as incorrect, "O inverno passo" As an educator, I think the rules regarding acceptable answers should be less strict.
Yes, you're right. However you have to bear in mind this is a computer software and it doesn't possess the ability to give you a break unless you program it. I think the company is aware of what you say, which is why they let you off easy with the tildes. The problem is that programming exceptions is difficult because there are so many and you have to include them one at the time.
I don't think they have to program every exception. The software analyzes your sentence, compare it to a set of correct translations, and figure out whether your error was a single letter or not.
However, that isn't the issue. The issue is that 'passo' is a word in portuguese, and the software can't be sure that you didn't put it there on purpose, resulting in an incorrect translation. When I make small spelling errors, the software lets me off the hook if it isn't a different word entirely.
Do you want to hand out participation ribbons just for trying??? Passo is 1st person singular present tense. You got the answer wrong, learn from it and move on. The point of this course is to learn a language; not to score the most number of imaginary points. If DL were to mark your answer correct, they'd be doing everyone trying to learn Portuguese a huge disservice.