The lesson “rolls back”?!

So, I am just successfully finishing my lesson, receive all the points and bonuses.

When the screen goes back to the “learning path”, I see how the “green circle” around my current lesson block goes smaller, and the lesson I just completed is “unlearned” again.

In the block of 6 lessons that bug appears once or twice, so to finish it I need to pass not 6 but 8 lessons.

Does someone else have such a problem?