Here's CFL Head of Officiating Tom Higgins reply to a fan with a similar question about the TSN time clock, which explains the confusion:
Q from Terry: I have noticed game in, game out that the clock keeps running after the whistle goes, 3,4,5 seconds before it stops. Nothing is done, except it seems in the final couple of minutes and then only occasionally. In one game I clocked almost 3 minutes, that’s enough time to run several plays, which would have a bearing on the out-come of the game. Does anyone pay attention during the game?
TH: Some of the confusion around the “clock? stems from the way it is presented on our broadcasts. TSN uses what television people call a “bug?. It’s a graphic representation of a clock and it’s operated by a TSN staffer who is doing his or her best to mimic what the actual official timekeeper is doing. Sometimes, like any of us, he or she makes a mistake.
And on your screen you then see the clock continue to tick. But you’re not seeing the official game clock. That’s the one that fans in the stands see on the scoreboard and it’s operated by the CFL appointed official timekeeper. In some leagues, the broadcaster plugs its clock into the official game clock, so they’re perfectly in synch.
It’s a long, technical story but the bottom line is that hasn’t been possible, in part because of the limitations posed by some of our older stadiums. We hope to fix it as new technology becomes available to us and we move into new facilities in several of our cities.