EDIT: Okay I see it. Strange because if you look at the contacts example program the comboboxes there seems to position correct.
This will be interesting to debug.
Okay, it's not really a bug. With this widget set a combobox will center itself vertically in its height. You do not specify the height of the list that appears when you click on the button. Perhaps this will change in the future. I will need to set LB5 for now to ignore that height value to make it backwards compatible with LB4, etc.
So, change the height to a smaller value such as 25 to resolve this in your programs.