Bug 329930 Resetting a perspective while its active part is not defined in the perspective causes the perspective to not have an active part after the reset
1. Window > Show View > Console 2. Window > Reset Perspective... > OK 3. No parts are active.
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/PartActivationHistory.java
* 
	 * @param part
	 *            the part to possibly add to the end of the activation history
	 */
	void append(MPart part) {
		if (!generalActivationHistory.contains(part)) {
			generalActivationHistory.addLast(part);
		}
	}
	/**
	 * Adds the specified part to the front of the activation history.
	 * 
	 * @param part
	 *            the part to insert into the front of the activation history
	 */
	void prepend(MPart part) {
		generalActivationHistory.remove(part);
		generalActivationHistory.addFirst(part);
	}
	/**
	 * Checks to see if this element and its parents are actually being rendered.
	 */
	private boolean isValid(MUIElement element) {
		if (element == null || !element.isToBeRendered() || !element.isVisible()) {
			return false;
		}
		if (element instanceof MApplication) {
			return true;
		}
		MUIElement parent = element.getParent();