The number of items in the dropdown list is not correct.
The number of items visible in a dropdown list does not correspond to the value in the settings.
This occurs when you the Use Windows XP Visual Styles setting is enabled and the you set the number of items in the dropdown list to a value greater than 8 and less than 30.
This appears to be a bug in the way Windows handles programs using Visual Styles and there is no known fix for this bug.