Bug 93245 [Dialogs] Error messages show up in two locations in the properties dialog
Force an error message: 1) select a Java project 2) open the properties dialog 3) navigate to Java Compiler>Building 4) enable project specific settings 5) enter a letter into the maximum number of problems field ->the error message shows up at the bottom 6) resize the dialog ->the error message also shows up in the banner
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferencePage.java
*  or <code>null</code> if none
     */
    protected PreferencePage(String title, ImageDescriptor image) {
        super(title, image);
    }
    /**
     * Computes the size for this page's UI control.
     * <p>
     * The default implementation of this <code>IPreferencePage</code>
     * method returns the size set by <code>setSize</code>; if no size
     * has been set, but the page has a UI control, the framework
     * method <code>doComputeSize</code> is called to compute the size.
     * </p>
     *
     * @return the size of the preference page encoded as
     *   <code>new Point(width,height)</code>, or 
     *   <code>(0,0)</code> if the page doesn't currently have any UI component
     */
    public Point computeSize() {
        if (size != null)
            return size;
        Control control = getControl();
        if (control != null) {
            size = doComputeSize();
            return size;
        }
        return new Point(0, 0);
    }
    /**
     * Contributes additional buttons to the given composite.