Bug 320285 Messages inteneded for developers in the error log
The message "unsupported: isEditorAreaVisible" appears in the error log during the normal run of e4 SDK. (For instance, starting the e4 SDK on an clean workspace produces two of those messages.)
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/ModelServiceImpl.java
if (leavePlaceholder) {
			MPlaceholder ph = MAdvancedFactory.INSTANCE.createPlaceholder();
			ph.setRef(element);
			curParent.getChildren().add(curIndex, ph);
		}
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see
	 * org.eclipse.e4.ui.workbench.modeling.EModelService#swap(org.eclipse.e4.ui.model.application.
	 * MUIElement, org.eclipse.e4.ui.model.application.MPlaceholder)
	 */
	public void swap(MPlaceholder placeholder) {
		MUIElement element = placeholder.getRef();
		MElementContainer<MUIElement> elementParent = element.getParent();
		int elementIndex = elementParent.getChildren().indexOf(element);
		MElementContainer<MUIElement> phParent = placeholder.getParent();
		int phIndex = phParent.getChildren().indexOf(placeholder);
		
		elementParent.getChildren().remove(element);
		phParent.getChildren().remove(placeholder);
		
		boolean onTop = element.isOnTop();
		boolean vis = element.isVisible();
		boolean tbr = element.isToBeRendered();
		element.setOnTop(placeholder.isOnTop());
		element.setVisible(placeholder.isVisible());
		element.setToBeRendered(placeholder.isToBeRendered());
		placeholder.setOnTop(onTop);