I thought it is pretty identical from the passenger's point of view when happening on the US soil - they lock you up, then put on the flight back. You are not free to go.

Would the same happen during preclearance in Canada in case you are denied entry, or are you free to go immediately?

There are no arrest warrants or civil judgements in our case. He never got in trouble with the law, in the US or otherwise. We are guessing his troubles are some kind of informal US retaliation for human rights issues in Russia, but it is just a guess. He just gets harassed every time he deals with US immigration, his visas are always issued so late that he misses the beginning of conferences he is scheduled to attend, and an immigration officer once let it slip out that there was "something" in the computer.