Bug 202121 setDateFormat does not working
If you want to set date format of the table column style you have to use setDateTimeFormatCategory and setDateTimeFormat instead of setDateFormatCategory and setDateFormat. If you will try to use setDateFormatCategory in the first case in xml-source you will see that your style contains dateFormat property. This property is not working at all, in the second case in xml-source you will see that your style contains dateTimeFormat property. I think it will be better if the result of setDateTimeFormatCategory and setDateFormatCategory will be the same.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/css/engine/StyleConstants.java
final int STYLE_VISIBLE_FORMAT = 1 ;
	final int STYLE_LINE_HEIGHT = 2 ;
	final int STYLE_BACKGROUND_REPEAT = 3 ;
	final int STYLE_BACKGROUND_ATTACHMENT = 4 ;
	final int STYLE_DATE_FORMAT = 5 ;
	final int STYLE_CAN_SHRINK = 6 ;
	final int STYLE_TEXT_OVERLINE = 7 ;
	final int STYLE_TEXT_UNDERLINE = 8 ;
	final int STYLE_BACKGROUND_IMAGE = 9 ;
	final int STYLE_BORDER_TOP_STYLE = 10 ;
	final int STYLE_BORDER_LEFT_STYLE = 11 ;
	final int STYLE_BORDER_RIGHT_STYLE = 12 ;
	final int STYLE_BORDER_BOTTOM_STYLE = 13 ;
	final int STYLE_COLOR = 14 ;
	final int STYLE_BORDER_TOP_WIDTH = 15 ;
	final int STYLE_TEXT_LINETHROUGH = 16 ;
	final int STYLE_BORDER_LEFT_WIDTH = 17 ;
	final int STYLE_BORDER_RIGHT_WIDTH = 18 ;
	final int STYLE_BORDER_BOTTOM_WIDTH = 19 ;
	final int STYLE_BACKGROUND_COLOR = 20 ;
	final int STYLE_BORDER_TOP_COLOR = 21 ;
	final int STYLE_BORDER_LEFT_COLOR = 22 ;
	final int STYLE_BORDER_RIGHT_COLOR = 23 ;
	final int STYLE_BORDER_BOTTOM_COLOR = 24 ;
	final int STYLE_LETTER_SPACING = 25 ;
	final int STYLE_TEXT_ALIGN = 26 ;
	final int STYLE_FONT_WEIGHT = 27 ;
	final int STYLE_FONT_VARIANT = 28 ;
	final int STYLE_NUMBER_FORMAT = 29 ;
	final int STYLE_VERTICAL_ALIGN = 30 ;