Place a Combobox on a form, bind it to a variable, property, or field.
Select dropdown list style.
Select 1 (value) for RowSourceType.
Enter a list, e.g. "One,Two,Three,Four" for RowSource.
Run the form.

Open the drop down list with the space bar.
Use the up and down arrow to position to an item. This works.

Now use the mouse to select from the drop down list.
Reopen the drop down list with the space bar.
Try the up and down arrow keys - they fail to move up and down the list properly.