categoryModel.IsExpanded doesn't work

Hi !

I wanted to have all my categories collapsed by default so I tried something like

protected override ICategoryModel CreateCategoryModel(string name, IDataFactoryRequest request)
{
 var categoryModel = base.CreateCategoryModel(name, request);
 categoryModel.IsExpanded = false;
 return categoryModel;
} 

 in my dataFactory, but it doesn't work.

What do I do wrong ?