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.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
public int getActivated() {
			return activated;
		}
		public int getDeactivated() {
			return deactivated;
		}
		public int getHidden() {
			return hidden;
		}
		public int getVisible() {
			return visible;
		}
		public boolean isValid() {
			return valid;
		}
		public List<MPart> getActivatedParts() {
			return activatedParts;
		}
		public List<MPart> getDeactivatedParts() {
			return deactivatedParts;
		}
		public List<MPart> getHiddenParts() {
			return hiddenParts;
		}
		public List<MPart> getVisibleParts() {
			return visibleParts;
		}
		public void partActivated(MPart part) {
			if (valid && part == null) {
				valid = false;