When DropDownWidth = 0, the width of the dropdown should autosize to the max. needed width for the fonts displayed in the dropdown. This is what I see here.
When DropDownWidth is configured to another value, I see that this width is used here, regardless of the control with or dropdown content size.
This was tested here with a default TAdvOfficeFontSelector on the form and I could not see an unexpected behavior in this regard.