The MPs were apparently expecting Conservative MP Diane Ablonczy to address the House. When she didn't show up, the Speaker moved on to the budget, catching the small smattering of MPs in the chamber off guard.
Not realizing they were voting on the budget at third reading, the Liberals and NDP sat quietly, enabling the measure to pass without challenge.
http://www.canada.com/nationalpost/news/story.html?id=76b0c325-d78a-4f77-8bbd-f435cda9b188&k=57102
Note: http://www.canada.com/n...

We've known for years that some MP's rarely show up in the House. What we see on TV during "question period" (similar to, but not to be confused with "Entertainment Tonight") is people sitting behind and beside the main characters. The TV rarely shows us the many many empty seats.
I guess the blame for this needs to be laid on the party whips (I almost typed "whoops"). It is their duty to know what is on the Agenda, and how important the matters are. If the Liberal and NDP whips had done their jobs, maybe this would not have happened.
So maybe some heads will roll. But on the other hand, this may have been a set-up by the Conservatives.
And then I started thinking: Canadian history would have been much different if this had happened with the budget of Joe Clark's government (on the 6th of December, 1979.)