How do you disable sorting a GtkTreeSortable

["Matthew Yaconis" <myaconis nycap rr com>]

I'm sure I'm missing something easy but I want to disable sorting when inserting and updating rows in a list 
store.  How is this accomplished?  I tried setting the default sort function to NULL and setting the column 
id to GTK_...DEFAULT_SORT... but it didn't help.

Thanks.