Android :: Way To Extend An ArrayAdapter?

I'm running into difficulties overriding an ArrayAdapter to be displayed in a ListActivity. The ArrayAdapter is filled asynchronously. What I'm trying to do is add a special "sentinel" object that sits at the beginning of the list to show the progress of the computation. Ultimately this may be a progress bar, but right now I am just using a TextView as a placeholder. The problem is that the sentinel seems to get inserted multiple times into the list - not just once at the beginning. It *seems* to be appearing once per "page" of list data (so if 8 list items fit on the screen, my sentinel appears as the 1st, then 9th, then the 17th, etc..), but that interpretation may not be accurate. While maybe not how ArrayAdapters were intended to be extended, I thought something like this should work by simply overriding getView() to show my custom TextView for index.