Run a script which generates a list window with the object type in one column. Have the list originally sort on one of the other columns.

Click on the Type column heading. It shows the little up-arrow to show sorting, but doesn't sort. Click on the Type column again, and the down-arrow appears and the list does sort.

It's not just the first click -- clicking on, say, Name sorts the first time. And if you go back and click on Type a 3rd time (back to the up-arrow), it doesn't change the sorting (the rows are still sorted in reverse alphabetical order).

Fixed.