GridLookUpEdit displays an empty list on filtering and redisplaying the list

If you edit the value in a GridLookUpEdit so that no match exists in the list, then display the list it will bring up an empty list. If you then close the popup and display it again you get the full unfiltered list. This is very confusing to the end user.

Steps to Reproduce:

Run the attached project

Type the value 'b' in the GridLookUpEdit control

Press F4 to display the list - it is empty

Press F4 again to close the popup

Press F4 to display the list again - this time all the value are shown

P.S. It doesn't matter how you display the popup (keyboard or mouse), the behaviour is always the same.

Actual Results:

First list is empty, the 2nd shows all values, yet nothing has been changed in the editor.

Expected Results:

The first time the popup is displayed it should show all values (with none selected) as it currently does the 2nd time it is displayed. This indicates to the user that their value is not valid, but gives them a list of vaild values to select from.