This is not by design =). I read a lot about category tree control and know how configure this control. Yes I set as RootCategory = "Рейтинг студентов" but also I set property ShowRootCategory="false". In my other pages on web site Categories Tree control works fine with same properties. Problems appear only with this categories. I describe you once more time this problem which cannot be resolve by configuration Category Tree control in Admin Interface:
As you can see I have a root category "Рейтинг студентов" which I use in property RootCategory of my Categories Tree control. My last added category ("Рейтинг на 27 июня 2008 года") does not show on site but It has some linked content. I found that adding other category without content but with same shorter name ("Рейтинг на 27 июня 2008г") fixed all. If I add after this new category It also does not show on site. I need to add other empty category to show my category with content on site.
At the first time I also think that this is design bug but when I look on source of my page I have not found any category which should be shown (I thought that It does not shown because Root Category take It place on div and this category lie below).