I've found a part workaround - put a space.  This has pros and cons:

Pros

     - a space keeps the drop down menu (your own description doesn't) and;

     - when users click on the textbox, the space is highlighted enabling overwriting without the need to delete the space first.

Cons

     - the space highlights everything that has a space, no this may not be a good solution if your descriptions have spaces.

If you know the answer, do post it here.