Bug 318363 [UI] Closing Perspectives changes others
If you open the Debug perspective and then close it the Package Explorer disappears. Root cause was that I opened the second perspective using the perspective switcher which performed the operation 'locally' rather than going through the WorkbenchPage#setPerspective code. This meant that the 'openPerspectives' list wasn't updated which meant that the 'closePerspective' call delegated to 'closeAllPerspectives' since it thought there was only one open.
bundles/org.eclipse.e4.ui.workbench.addons.swt/src/org/eclipse/e4/ui/workbench/addons/minmax/TrimStack.java
private static Image restoreImage;
	private ToolBar trimStackTB;
	MPartStack theStack;
	private Composite hostPane;
	ControlListener caResizeListener = new ControlListener() {