Okay I was working on testing the Autocomplete Extender on a site I am working on.  I noticed something interesting when testing the search functionality.  Take a look at what was going on:

As you can see, the SKU codes I was looking for started with "TEST". But if a bunch of junk text was included before the actual SKU, it would stay with it in the dropdown list.  I finally found the solution by removing the "DelimiterCharacters" from the control.  I hope this works for you!

On an unrelated note I accepted a full time position at Blue Horseshoe Solutions today, I am thrilled.