OK, so I clicked the Numbers section, but instead of starting the first lesson, I opened a discussion. I used the back button in my browser to get back to the Numbers section overview, and it seemed to not load right away, so I clicked the back button again, I think I may have done some other back and forth stuff, and then lesson 1 of Numbers was marked as completed! What? I didn't even start it.
So, yeah, thought you oughtta know.