Hate to blow your mind, but I've determined many foreign passports presented at my border to be invalid, refused entry to the holder, and confiscated the document. See if you can think of any reasons for this. Sometimes we would retain the document permanently, other times it would be returned to the Embassy or given to the plane's Purser with instruction to pass to Immigration only at the home Port. The airline had an obligation to remove a person refused entry on the next available flight, so, when it was necessary, I would issue an ICAO travel document for that travel. Some may call it harassment to question passengers or refuse entry to the worlds criminal refuse; others understand that not all travellers have benign motives.