Black Backround in disabled combobox

Hi;

I created a control that is parent of other controls. One of the children is a combo box with style CBS_DROPDOWNLIST.
Whenever the control is disabled in a skinned application the background of the control is black:

 

When I remove my .\styles folder and restart the application the app is no longer skinned, but the combobox is drawn as expected.

How can I get the same result in the skinned app?
In this case I use Toolkit 18.3

TIA

Hello Martin,

And what was the solution ?

Regards,
 Oleksandr Lebed