When I open a course (not sure it is called so in English) I’m expecting to see all the lessons of it. Some months ago it was so, as I remember. But now the list of the lessons in each course depends on the levels chosen on the left check boxes.
For me it looks a bit strange. The lessons in a course are usually connected to each other, that’s why it has not too much sence to select just some of them.
Sometimes the courses have lessons with different levels within. For example, they may begin with A2 lessons and than have B1-B2 lessons in the middle. While I’m interested just in the Intermediate level, I cannot see the begining of the course. I need to switch on the Beginers levels on the left to be able to see the whole course’s content.
Here is an example where I discovered the number of the lessons is bigger than I could see with my current levels settings: http://www.lingq.com/learn/de/library/courses/39528/
The worst situation may happen when some of the lessons do not have a level assigned.
Good find. I’ve never thought of this. I’ve some courses too with lessons of different levels.
I think the "problem"are the left check boxes.
Some weeks ago the filter for courses were empty,
so I could see the whole courses 
now it is beginner 1 and 2.
I must them making empty each time from hand.
next day it is still Beginner 1 and 2.
j;-)