Yes, this happened to me at YUL with my family as well, using Nexus. As I recall from YUL, yes, you exit right at the ramp to baggage claim, but you should go back into the Dimplomatic line and see an agent, like YYZ. The agent should ask you the question of what you brought, and make the mark.

In my case, I did that, told the agent about the chocolate and candy, and the agent marked on all of our NEXUS sheets. We got to the exit, and bam - sent into secondary for a 60 minute wait, too. When we got to the front, we put the bags on the counter, the agent asked us what we had, and we told him the same thing as the desk - he said next time we should go to the desk for the agent to mark the form, and told us to just go ahead and leave without inspection. I said we did, and he just shrugged.

It just seems to be ridiculous at YUL.... at YOW and YYZ I always do the same, and like you the agents just mark my form with the "all clear" code, and I exit without a problem. I bring a bag of almonds with me for snack and gum - and I do not want to risk my Nexus.

For GE, same thing - I get the O on the card, tell the agents, and am sent on.

Looks like YUL is the gong show...