Order By with a filter

Hi I have a ListView that has 3 columns of Category , Title and Description so there are lots of titles and descriptions within each category.

I also have a drop down to allow filtering by Category. On entry, no Category is selected so the ListView shows all Categories, Titles and Descriptions. When the user selects a Category in the dropdown, the listview is filtered properly and is ordered by Description.

The problem I have is that the ORDER BY for the ListView collection does not allow me to include Category because the data has a filter of Category so I can only order by Description. This is fine when the filter is set but when the user clears the Category filter, the listview is just in order of description and I need it to be description within Category.

Can anyone suggest a way I can achieve this?