Stoned,
Here are some more details about my friend.
Came here on F1. Always in Status. Graduated with Bachelors from US University. Got a job in a major corporation and applied for H1. Around the second year of H1 he went to Mexico and got H1 visa stamp. He then visited Pakistan later that year and returned back within a month from vacation.
He renewed his H1 for additional 3 years. Since the visa he got from Mexico expired with first H1 he sent his passport for restamping to St Louis. This was during the days St Louis was stopping to do internal revalidation, and they sent him his passport back asking him to apply from a visa from a consular post outside the US. My friend didnt leave US again till Canada landing trip.
Unfortunately my friend lost his passport a few months before he received request for Canada landing stamp and therefore had to apply for and received brand new Paki passport from Pak Embassy in Washington DC. He sent this passport to Canadian consulate and got landing stamp.
He then went and completed his landing. Did not even go near US Consulate or Embassy
. When trying to enter US again (at Niagara Falls) he was not allowed to enter US and was told to go back and apply for a new visa. Reasons given were the following
1) He didnt do exit registration while leaving US. (Though my friend says that when entering Canada by road he didnt see any US post where he could do exit registration).
2) He should apply for security clearance from state dept.
3) His passport was blank and did not have any expired USA visa (though he is not sure if that was just excuse or genuine, since he had copies of his expired visas).
When he was sent back to Canada Immigration post, the officer there said that it happened quite frequently, and if he wasnt a PR than Canada would have to deport him depending on his visa so he was lucky for having the PR.
He then tried to contact US immigration office at Toronto Pearson airport but they told him he needs to apply for visa also.
Of course my friend is very bitter from the experience, and I dont want to give out his info to protect his privacy. Please let me know if you have any additional q's.