wxPython - ListCtrl ColumnSorterMixin sometimes works sometimes doesn't!

[Steve Senior]

Hi,

My application has a tree control in which a user can select a filter. 
This filter is then applied to the results and the results are 
constructed in the ListControl (report style) widget.

This all works fine.

Recently I added the wx.lib.mixins.listctrl.ColumnSorterMixin mixin to 
the ListCtrl widget.

Now here is the problem. On some of the filters you can sort all of the 
columns both ascending and descending - i.e. if you click a column once 
it will sort properly, then if you click the column again it will 
happily reverse the sort.

On some of the filters you can only sort the column once. Repeated 
clicks do not reverse the sort order. I added some print statments to 
the listctrl.py to see what was happening here and it appears that when 
you click the column for the second time, it actually sorts it twice 
which means that the display doesn't change!

This is really perplexing me, I've exhausted all of my options and need 
some help please.

Many Thanks,
Steve.