The lesson browsing page for the learning center has been working weirdly these past few days (I guess that's a left-over from August 9 maintenance...).
Basically, it won't memorize filters for lesson categories, and number of row displayed, and sometimes several months's worth of lessons just disappear (though they can still be studied if you use the drop-down menus).
The worst part of this is that it's completely random... I was studying some 2007 lessons yesterday evening, and all of the sudden when I got back to the main page, they were gone from the list (which had been fine only a few minutes earlier). As for the filters, I can never know what will show up and what I'll have to check...
I hope you can fix this !