Not working for me.
even though when i look at the datatable on the "RadGrid1.DataSource = AddPriorityField(originalSource);" line the table has the priority row with the right value, once the page loads the priority column comes up as "0" for everything.
one difference i notice is in your sample you "GetGridData" everytime, but i am storing the initial data in httpcontext.current.cache. I am pulling large amounts of data from SQL and dont want to query it every time they sort by the priority column.
my feeling is that this is the problem, because if i do re-query from the database it does work. any way around this?