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_MARGIN_LEFT = 31 ;
	final int STYLE_MARGIN_RIGHT = 32 ;
	final int STYLE_DISPLAY = 33 ;
	final int STYLE_TEXT_TRANSFORM = 34 ;
	final int STYLE_BACKGROUND_POSITION_Y = 35 ;
	final int STYLE_PADDING_LEFT = 36 ;
	final int STYLE_PADDING_RIGHT = 37 ;
	final int STYLE_FONT_SIZE = 38 ;
	final int STYLE_FONT_STYLE = 39 ;
	final int STYLE_WHITE_SPACE = 40 ;
	final int STYLE_ORPHANS = 41 ;
	final int STYLE_MASTER_PAGE = 42 ;
	final int STYLE_STRING_FORMAT = 43 ;
	final int STYLE_WORD_SPACING = 44 ;
	final int STYLE_BACKGROUND_POSITION_X = 45 ;
	final int STYLE_PAGE_BREAK_BEFORE = 46 ;
	final int STYLE_PAGE_BREAK_INSIDE = 47 ;
	final int STYLE_SHOW_IF_BLANK = 48 ;
	final int STYLE_FONT_FAMILY = 49 ;
	final int STYLE_NUMBER_ALIGN = 50 ;
	final int STYLE_PAGE_BREAK_AFTER = 51 ;
	final int STYLE_MARGIN_BOTTOM = 52 ;
	final int STYLE_MARGIN_TOP = 53 ;
	final int STYLE_WIDOWS = 54 ;
	final int STYLE_PADDING_BOTTOM = 55 ; 
	final int STYLE_PADDING_TOP = 56;
	
	final int NUMBER_OF_STYLE = 57;
}