Is there are reason why using the feminine versions of these words is wrong?
When we are generalizing things on Portuguese, we use the masculine words.
Where's the generalization in it?
There is no noun. We're generalizing. Most Romance languages default to masculine. It's a remnant of Roman sexism.
Hebrew also defaults to masculine. And historically, English has too, although singular they has been fairly universally adopted in colloquial speech.
Is using "comprido" instead of longo incorrect?
quem é que sabe? Não pode ser?
Pode... it's possible
Shouldn't sei lá be accepted for who knows here?
I have exactly what you have but it is marked wrong. Why?