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/content/IStyle.java
public String getTextOverline( );
	public String getTextLineThrough( );
	public String getMasterPage( );
	public String getShowIfBlank( );
	public String getCanShrink( );
	public String getStringFormat( );
	public String getNumberFormat( );
	public String getDateFormat( );
	public String getNumberAlign( );
	public String getVisibleFormat( );
	public void setBackgroundPositionX( String x ) throws DOMException;
	public void setBackgroundPositionY( String y ) throws DOMException;
	public void setTextUnderline( String underline ) throws DOMException;
	public void setTextOverline( String overline ) throws DOMException;
	public void setTextLineThrough( String through ) throws DOMException;
	public void setMasterPage( String page ) throws DOMException;
	public void setShowIfBlank( String blank ) throws DOMException;
	public void setCanShrink( String shrink ) throws DOMException;
	public void setStringFormat( String format ) throws DOMException;
	public void setNumberFormat( String format ) throws DOMException;
	public void setDateFormat( String format ) throws DOMException;
	public void setNumberAlign( String align ) throws DOMException;
	public void setVisibleFormat( String visibility ) throws DOMException;
	public CSSValue getProperty( int index );
	public void setProperty( int index, CSSValue value );
	public void setProperties( IStyle style );
	public String getCssText( int index );
	public void setCssText( int index, String value ) throws DOMException;
	boolean isEmpty( );
}