Index: src/wp-includes/class-wp-customize-manager.php
===================================================================
--- src/wp-includes/class-wp-customize-manager.php	(revision 36252)
+++ src/wp-includes/class-wp-customize-manager.php	(working copy)
@@ -1579,9 +1579,13 @@
 	 */
 	public function get_return_url() {
 		$referer = wp_get_referer();
+
+		//Exclude following files from referer.
+		$exclude_referer = array( 'customize.php', 'wp-login.php' );
+
 		if ( $this->return_url ) {
 			$return_url = $this->return_url;
-		} else if ( $referer && 'customize.php' !== basename( parse_url( $referer, PHP_URL_PATH ) ) ) {
+		} else if ( $referer && !in_array( basename( parse_url( $referer, PHP_URL_PATH ) ), $exclude_referer ) ) {
 			$return_url = $referer;
 		} else if ( $this->preview_url ) {
 			$return_url = $this->preview_url;