John Calvin ""There have been certain folk who have wished to suggest from this passage [Matt 1:25] that the Virgin Mary had other children than the Son of God, and that Joseph had then dwelt with her later; but what folly this is! For the gospel writer did not wish to record what happened afterwards; he simply wished to make clear Joseph's obedience and to show also that Joseph had been well and truly assured that it was God who had sent His angel to Mary. He had therefore never dwelt with her nor had he shared her company... And besides this Our Lord Jesus Christ is called the first born. This is not because there was a second or a third, but because the gospel writer is paying regard to precedence. Scripture speaks thus of naming the first-born whether or not there was any question of the second." (Sermon on Matthew)
Martin Luther "He, Christ, our Savior, was the real and natural fruit of Mary's virginal womb . . . This was without the cooperation of a man, and she remained a virgin after that." (Sermons on John, chapters 1-4, 1537-39)
Protestants understand that their leaders' statements/interpretations can be fallible. Catholics don't seem to understand this...it's foreign thinking for them.