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/BuildAction.java
/**
 * Creates a new action of the appropriate type. The action id is 
 * <code>ID_BUILD</code> for incremental builds and <code>ID_REBUILD_ALL</code>
 * for full builds.
 *
 * @param shell the shell for any dialogs
 * @param type the type of build; one of
 *  <code>IncrementalProjectBuilder.INCREMENTAL_BUILD</code> or 
 *  <code>IncrementalProjectBuilder.FULL_BUILD</code>
 */
public BuildAction(Shell shell, int type) {
	super(shell, "");
	if (type == IncrementalProjectBuilder.INCREMENTAL_BUILD) {
		setText(IDEWorkbenchMessages.getString("BuildAction.text")); 
		setToolTipText(IDEWorkbenchMessages.getString("BuildAction.toolTip")); 
		setId(ID_BUILD);
		WorkbenchHelp.setHelp(this, IHelpContextIds.INCREMENTAL_BUILD_ACTION);
	}
	else {
		setText(IDEWorkbenchMessages.getString("RebuildAction.text")); 
		setToolTipText(IDEWorkbenchMessages.getString("RebuildAction.tooltip")); 
		setId(ID_REBUILD_ALL);
		WorkbenchHelp.setHelp(this, IHelpContextIds.FULL_BUILD_ACTION);
	}
		
	this.buildType = type;
}
/* (non-Javadoc)
 * Method declared on WorkspaceAction.
 */