Bug 118644 Hint for Date Time Parameters
The hint you give for date time parameters (Please enter date ... pattern: MM/DD/YYYY ....) is only true if the date is unformatted. If you apply a format, you must enter it according to it. So it's quite confusing!
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ParameterDialog.java
if ( formatPattern != null )
				{
					displayFormat += ": " + formatPattern; 
				}
				if ( type.equals( DesignChoiceConstants.PARAM_TYPE_DATETIME ) )
				{
					previewString = new DateFormatter( formatPattern == null ? formatCategroy
							: formatPattern,
							Locale.getDefault( ) ).format( new Date( ) );
				}
				else if ( type.equals( DesignChoiceConstants.PARAM_TYPE_STRING ) )
				{
					previewString = new StringFormatter( formatPattern == null ? formatCategroy
							: formatPattern,
							Locale.getDefault( ) ).format( "Sample" ); 
				}
				else
				{
					previewString = new NumberFormatter( formatPattern == null ? formatCategroy
							: formatPattern,
							Locale.getDefault( ) ).format( 123456789.01234 );
				}
			}
		}
		formatField.setText( displayFormat );
		previewLabel.setText( previewString );
		changeFormat.setEnabled( choiceSet != null );
	}
	private String getCategroy( String formatString )
	{