What behavior are you expecting here? If the fixed columns fill the entire width of the grid, there's nothing to scroll.

I guess it would be nice if the grid had a property that allowed you to set a limit to the maximum width of the fixed column and then displayed a scrollbar on the left when necessary, but there's currently no such feature in the grid, so it's pretty much up to you to make sure that the user can make the grid bigger or the column smaller in a case like this.