Bug 134266 [Wizard] Page description not set if page message already set
Since page messages such as errors and warnings used to be displayed in the same widget as the page description, code was put in place in WizardDialog#updateDescriptionMessage() to avoid setting the page description if there was already a message. As of 3.2 M6 there is a separate widget for displaying error and warning messages and so the page description should always be set.
bundles/org.eclipse.jface/src/org/eclipse/jface/wizard/WizardDialog.java
/**
     * Update the message line with the page's description.
     * <p>
     * A discription is shown only if there is no message or error message.
     * </p>
     */
    private void updateDescriptionMessage() {
        pageDescription = currentPage.getDescription();
        if (pageMessage == null) {
			setMessage(currentPage.getDescription());
		}
    }
    /* (non-Javadoc)
     * Method declared on IWizardContainer.
     */
    public void updateMessage() {
        if (currentPage == null) {
			return;
		}
        pageMessage = currentPage.getMessage();
        if (pageMessage != null && currentPage instanceof IMessageProvider) {
			pageMessageType = ((IMessageProvider) currentPage).getMessageType();
		} else {
			pageMessageType = IMessageProvider.NONE;
		}
        if (pageMessage == null) {
			setMessage(pageDescription);
		} else {
			setMessage(pageMessage, pageMessageType);
		}