Bug 127519 [Markers] Disabling all filters gives empty list
If you disable (uncheck) the 'Default' filter then the result seems to be that -everything- gets filtered. This seems most unintuitive...I'd think that if I don't have any filters enabled then I should see an 'unfiltered' list.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/views/markers/internal/MarkerAdapter.java
* Return whether or not the receiver has markers without scheduling
	 * anything if it doesn't.
	 * 
	 * @return boolean <code>true</code> if the markers have not been
	 *         calculated.
	 */
	public boolean hasNoMarkers() {
		return lastMarkers == null;
	}
	/**
	 * Return the categories for the receiver.
	 * 
	 * @return MarkerCategory[] or <code>null</code> if there are no
	 *         categories.
	 */
	public MarkerCategory[] getCategories() {
		if (building) {
			return null;
		}
		return categories;
	}
	/**
	 * Return whether or not the receiver is building.
	 * @return boolean
	 */
	boolean isBuilding() {
		return building;
	}
}