Bug 329184 Detached view that is an activation target candidate can prevent perspective switching
1. Detach the 'Outline' view. 2. Window > Open Perspective > Debug 3. Window > Open Perspective > Java 4. The perspective switch doesn't actually happen. You see the 'Debug' perspective's content with an 'Outline' view detached. Closing the 'Outline' view in the 'Debug' perspective will workaround this problem.
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/PartActivationHistory.java
}
		} else if (parent instanceof MGenericStack && parent.getSelectedElement() != element) {
			
			return false;
		}
		return isValid(perspective, parent);
	}
	/**
	 * Determines whether this element is contained within an MArea, and to return the area if it
	 * is.
	 */
	private MArea isInArea(MUIElement element) {
		MPlaceholder placeholder = element.getCurSharedRef();
		if (placeholder == null) {
			MUIElement parent = element.getParent();
			if (parent == null) {
				
				parent = (MUIElement) ((EObject) element).eContainer();
			}
			return parent instanceof MApplication ? null : parent instanceof MArea ? (MArea) parent
					: isInArea(parent);
		}
		MUIElement parent = placeholder.getParent();
		if (parent == null) {
			
			parent = (MUIElement) ((EObject) placeholder).eContainer();
		}
		return parent instanceof MApplication ? null : parent instanceof MArea ? (MArea) parent
				: isInArea(parent);
	}