Index: src/wp-admin/includes/class-wp-users-list-table.php
===================================================================
--- src/wp-admin/includes/class-wp-users-list-table.php	(revision 25607)
+++ src/wp-admin/includes/class-wp-users-list-table.php	(working copy)
@@ -193,17 +193,8 @@
 		if ( ! $this->is_site_users )
 			$post_counts = count_many_users_posts( array_keys( $this->items ) );
 
-		$editable_roles = array_keys( get_editable_roles() );
-
 		$style = '';
 		foreach ( $this->items as $userid => $user_object ) {
-			if ( count( $user_object->roles ) <= 1 ) {
-				$role = reset( $user_object->roles );
-			} elseif ( $roles = array_intersect( array_values( $user_object->roles ), $editable_roles ) ) {
-				$role = reset( $roles );
-			} else {
-				$role = reset( $user_object->roles );
-			}
 
 			if ( is_multisite() && empty( $user_object->allcaps ) )
 				continue;
@@ -237,6 +228,8 @@
 		else
 			$url = 'users.php?';
 
+		$user_roles = $this->get_role_list( $user_object );
+
 		$checkbox = '';
 		// Check if the user for this row is editable
 		if ( current_user_can( 'list_users' ) ) {
@@ -260,16 +253,22 @@
 			$actions = apply_filters( 'user_row_actions', $actions, $user_object );
 			$edit .= $this->row_actions( $actions );
 
+			// Role classes.
+			$role_classes = esc_attr( implode( ' ', array_keys( $user_roles ) ) );
+
 			// Set up the checkbox ( because the user is editable, otherwise it's empty )
 			$checkbox = '<label class="screen-reader-text" for="cb-select-' . $user_object->ID . '">' . sprintf( __( 'Select %s' ), $user_object->user_login ) . '</label>'
-						. "<input type='checkbox' name='users[]' id='user_{$user_object->ID}' class='$role' value='{$user_object->ID}' />";
+						. "<input type='checkbox' name='users[]' id='user_{$user_object->ID}' class='$role_classes' value='{$user_object->ID}' />";
 
 		} else {
 			$edit = '<strong>' . $user_object->user_login . '</strong>';
 		}
-		$role_name = isset( $wp_roles->role_names[$role] ) ? translate_user_role( $wp_roles->role_names[$role] ) : __( 'None' );
+
 		$avatar = get_avatar( $user_object->ID, 32 );
 
+		// Comma-separated list of user roles.
+		$roles_list = implode( ', ', $user_roles );
+
 		$r = "<tr id='user-$user_object->ID'$style>";
 
 		list( $columns, $hidden ) = $this->get_column_info();
@@ -297,7 +296,7 @@
 					$r .= "<td $attributes><a href='mailto:$email' title='" . esc_attr( sprintf( __( 'E-mail: %s' ), $email ) ) . "'>$email</a></td>";
 					break;
 				case 'role':
-					$r .= "<td $attributes>$role_name</td>";
+					$r .= "<td $attributes>" . esc_html( $roles_list ) . "</td>";
 					break;
 				case 'posts':
 					$attributes = 'class="posts column-posts num"' . $style;
@@ -321,4 +320,37 @@
 
 		return $r;
 	}
+
+	/**
+	 * Generate an array of user roles for a given user object.
+	 *
+	 * @access protected
+	 * @since 3.7.0
+	 *
+	 * @param WP_User $user_object The WP_User object.
+	 * @return array An array of user roles.
+	 */
+	protected function get_role_list( $user_object ) {
+		global $wp_roles;
+
+		$role_list = array();
+
+		foreach ( $user_object->roles as $role ) {
+			if ( isset( $wp_roles->role_names[ $role ] ) )
+				$role_list[$role] = translate_user_role( $wp_roles->role_names[ $role ] );
+		}
+
+		if ( empty( $role_list ) )
+			$role_list['none'] = _x( 'None', 'no user roles' );
+
+		/**
+		 * Filter the returned array of roles for a user.
+		 *
+		 * @since 3.7.0
+		 *
+		 * @param array   $role_list   An array of user roles.
+		 * @param WP_User $user_object A WP_User object.
+		 */
+		return apply_filters( 'get_role_list', $role_list, $user_object );
+	}
 }