Bug 53582 Rebuild Project are not run in the background?
The "Build All" and "Rebuild All" actions are run in the background, but the "Build Project" and "Rebuild Project" actions aren't. This is not consistent and I was surprised to get a modal dialog when performing a "Rebuild Project".
bundles/org.eclipse.ui.ide/extensions/org/eclipse/ui/actions/WorkspaceAction.java
/**
	 * Multi status containing the errors detected when running the operation or
	 * <code>null</code> if no errors detected.
	 */
	private MultiStatus errorStatus;
	/**
	 * The shell in which to show the progress and problems dialog.
	 */
	private Shell shell;
	/**
	 * Creates a new action with the given text.
	 *
	 * @param shell the shell (for the modal progress dialog and error messages)
	 * @param text the string used as the text for the action, 
	 *   or <code>null</code> if there is no text
	 */