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
pageContainerLayout.minimumHeight = minHeight;
    }
    /**
     * Sets the minimum page size used for the pages.
     *
     * @param size the page size encoded as
     *   <code>new Point(width,height)</code>
     * @see #setMinimumPageSize(int,int)
     */
    public void setMinimumPageSize(Point size) {
        setMinimumPageSize(size.x, size.y);
    }
    /**
     * Sets the size of all pages.
     * The given size takes precedence over computed sizes.
     *
     * @param width the page width
     * @param height the page height
     * @see #setPageSize(Point)
     */
    public void setPageSize(int width, int height) {
        pageWidth = width;
        pageHeight = height;
    }
    /**
     * Sets the size of all pages.
     * The given size takes precedence over computed sizes.
     *
     * @param size the page size encoded as
     *   <code>new Point(width,height)</code>