The DropDownRows property indirectly controls the height of the dropdown window.
If the total number of items is greater than the DropDownRows property's value, a scroll bar will appear to scroll the dropdown window.
If the total number of items is smaller than the DropDownRows value, the dropdown window is shrunk to fit all items.
If an end-user has resized the dropdown vertically, this new height is applied the next time the dropdown is shown. The DropDownRows property is ignored in this case until you forcibly set a value to it.