Index: Gruntfile.js
===================================================================
--- Gruntfile.js	(revision 26888)
+++ Gruntfile.js	(working copy)
@@ -43,7 +43,16 @@
 			version: {
 				options: {
 					processContent: function( src ) {
-						return src.replace( /^(\$wp_version.+?)-src';/m, '$1\';' );
+						return src.replace( /^\$wp_version = '(.+?)';/m, function( str, version ) {
+						    version = version.replace( '-src', '' );
+
+							if ( /[^0-9.]+/.test( version ) ) {
+								// If the version is alpha|beta|RC
+								version += '-' + ( new Date() ).getTime();
+							}
+
+							return "$wp_version = '" + version + "';";
+						});
 					}
 				},
 				files: [
Index: src/wp-includes/script-loader.php
===================================================================
--- src/wp-includes/script-loader.php	(revision 26888)
+++ src/wp-includes/script-loader.php	(working copy)
@@ -50,8 +50,10 @@
 function wp_default_scripts( &$scripts ) {
 	include ABSPATH . WPINC . '/version.php'; // include an unmodified $wp_version
 
+	$is_src = ( false !== strpos( $wp_version, '-src' ) );
+
 	if ( ! defined( 'SCRIPT_DEBUG' ) )
-		define( 'SCRIPT_DEBUG', false !== strpos( $wp_version, '-src' ) );
+		define( 'SCRIPT_DEBUG', $is_src );
 
 	if ( ! $guessurl = site_url() ) {
 		$guessed_url = true;
@@ -65,6 +67,11 @@
 
 	$suffix = SCRIPT_DEBUG ? '' : '.min';
 
+	if ( $is_src ) {
+		// When running from /src refresh browser cache on every load
+		$scripts->default_version .= time();
+	}
+
 	$scripts->add( 'utils', "/wp-includes/js/utils$suffix.js" );
 	did_action( 'init' ) && $scripts->localize( 'utils', 'userSettings', array(
 		'url' => (string) SITECOOKIEPATH,
@@ -533,8 +540,10 @@
 function wp_default_styles( &$styles ) {
 	include ABSPATH . WPINC . '/version.php'; // include an unmodified $wp_version
 
+	$is_src = ( false !== strpos( $wp_version, '-src' ) );
+
 	if ( ! defined( 'SCRIPT_DEBUG' ) )
-		define( 'SCRIPT_DEBUG', false !== strpos( $wp_version, '-src' ) );
+		define( 'SCRIPT_DEBUG', $is_src );
 
 	if ( ! $guessurl = site_url() )
 		$guessurl = wp_guess_url();
@@ -547,6 +556,11 @@
 
 	$suffix = SCRIPT_DEBUG ? '' : '.min';
 
+	if ( $is_src ) {
+		// When running from /src refresh browser cache on every load
+		$styles->default_version .= time();
+	}
+
 	$rtl_styles = array( 'wp-admin', 'ie', 'media', 'admin-bar', 'customize-controls', 'media-views', 'wp-color-picker', 'wp-pointer', 'editor-buttons', 'farbtastic', 'wp-auth-check', 'wp-jquery-ui-dialog', 'media-views', 'buttons', 'install', 'colors-fresh' );
 
 	$styles->add( 'wp-admin', "/wp-admin/css/wp-admin$suffix.css", array( 'open-sans', 'dashicons' ) );