It was just a matter of time

So it's a long weekend in the US and Canada this weekend, and as such it's easy to let your mind go a bit soft while you're away from work. I know nothing of this, of course, as I'm still unemployed. All the same, I thought I might present you, my dear readers, with a little puzzle to think over to keep your mind fresh and active.

One of the upsides about doing job interviews is occasionally being presented with a very interesting logic puzzle. Of course, most of the puzzles are really rather mundane, and even the best ones tend to be quite contrived, so I thought I might pose a puzzle to you that is in fact drawn from my daily life.

You see, I have a digital clock in my kitchen that doesn't always tell the right time. Usually it's quite accurate, but often it's mysteriously a few minutes off. If you were to observe this clock for some time, you might notice that the rightmost digit for the minutes counts quite oddly. The sequence is: 0, 1, 2, 3, 4, 9, 8, 7, 8, 9, and then back around to 0 again to do it all over.

The cause of this bizarre acalculial malfunction is deceptively simple. Can you figure out what it is?