Bug 31556 Export jar from Navigator view fails
(M5 build) In Navigator view (resource perspective), right-click on a src/ directory containing your sources, select export->jar file and the package selector opens with no resource selected (and finish button disabled); but it seems that the src/ dir is really selected, because if you re-select it in the window, it ends up with a "jar creation failed" and a lot of duplicate entries in the error log. If you try the same from the Projects view (Java browsing perspective), it works fine.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/jarpackager/JarPackageWizardPage.java
}
	/*
	 * Overrides method from IJarPackageWizardPage
	 */
	public boolean isPageComplete() {
		boolean complete= validateSourceGroup();
		complete= validateDestinationGroup() && complete;
		complete= validateOptionsGroup() && complete;
		if (complete)
			setErrorMessage(null);
		return complete;
	}
	/*
	 * Implements method from Listener
	 */	
	public void handleEvent(Event e) {
		if (getControl() == null)
			return;
		update();
	}
	
	protected void update() {
		updateModel();
		updateWidgetEnablements();
		updatePageCompletion();
	}
	
	protected void updatePageCompletion() {	
		boolean pageComplete= isPageComplete();
		setPageComplete(pageComplete);