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/PartServiceImpl.java
&& partActivationHistory.isValid(perspective, activePart)) {
				MPart target = activePart;
				IEclipseContext activeChild = activePart.getContext().getParent().getActiveChild();
				if (activeChild != null) {
					activeChild.deactivate();
				}
				perspective.getContext().activate();
				modelService.bringToTop(target);
				activate(target, true, false);
				return;
			}
			MPart newActivePart = perspective.getContext().getActiveLeaf().get(MPart.class);
			if (newActivePart == null) {
				
				MPart candidate = partActivationHistory.getActivationCandidate(perspective);
				if (candidate != null) {
					modelService.bringToTop(candidate);
					partActivationHistory.activate(candidate, false);
					return;
				}
			}
			
			if (newActivePart == null) {
				modelService.bringToTop(perspective);
				perspective.getContext().activate();
			} else {
				activate(newActivePart, true, false);
			}
		}
	}