Yes, this would be the case. If you ever have to go to the USA again, carry a lot of documentation to prove you really left the country when you did (think ticket stubs from leaving Canada, bank statements, that kind of paperwork). Also include photocopies of this when sending in the green form, and mention as many exact dates and times in the accompanying letter as possible. (And add a copy of that letter to your paperwork when going to the USA.)
Even with all that I wouldn't be too surprised if they denied you entry. Immigration procedures for the USA suck bigtime.
Here's the official information:
I still have the I-94 or I-94W in my possession; what should I do?
If you have left the United States and are still in possession of the I-94 or I-94W it is in your best interest to forward it to the appropriate authorities so that your record is corrected and that you do not experience any problems on future travel to the United States as a result.
It is very important that you complete the back of the card listing the port of departure and date of departure from the United States and the carrier/flight information. The I-94 or I-94W together with a letter of explanation and evidence of your departure from the U.S. should be sent to:
ACS-USCBP, SBU, P.O. Box 7125
London KY 40742-7125
[ Edit: Edited on Oct 11, 2007, at 12:44 PM by Sander ]
Already writing a letter and add some copies of salary and entry/exit of other countries since then.
I found another adress though, on the visumdienst.nl website, which they gave me.
1300 Pennsylvania Avenue N.W
Washington DC 20229
I found yet a third address. However, this one was directly linked from the travel.state.gov website (while my previous answer was the result of a google search), and it seems current when navigating from the root of that CBP website. so I think this is the one you should consider authoritative.
Sorry for your woe man. Every time I have crossed between US and Canada I've had trouble.
Live and Learn
My b/f was threatened with arrest when we tried to get into the US from Canada and he still has his green visa card in his passport (he'd come in through the States but had left directly from Canada). The guard told him Canada Customs should have sent it back, else it was up to him to return it. In the end, he explained the stuation and they let him throug, but they were not happy.