I've read your article on combo & list - boxes in grids and studied the samples that you kindly provide.
Since you clearly are the expert here I hope you'll forgive me bothering you with this issue.

Nothing to forgive <s>. However, I am visiting family in England at the moment and do not have access to my materials

There is an undesirable side-effect, in that the selected data are only displayed correctly by using the mouse.
>When using the keyboard -which is the preferred method- the displayvalue, regardless of what was selected, is left blank when the listbox loses the focus.

I think that I described a very similar sitution in the white paper as well as the workarounds. If someone else has not yet provided a solution, I will get back to you when I have had a chance to look at this.