Index: formatting.php
--- formatting.php Base (BASE)
+++ formatting.php Locally Modified (Based On LOCAL)
@@ -1588,7 +1588,7 @@
  *
  * Requires and returns a date in the Y-m-d H:i:s format. Simply subtracts the
  * value of the 'gmt_offset' option. Return format can be overridden using the
- * $format parameter.
+ * $format parameter.
  *
  * @since 1.2.0
  *
@@ -1600,7 +1600,8 @@
 function get_gmt_from_date($string, $format = 'Y-m-d H:i:s') {
 	preg_match('#([0-9]{1,4})-([0-9]{1,2})-([0-9]{1,2}) ([0-9]{1,2}):([0-9]{1,2}):([0-9]{1,2})#', $string, $matches);
 	$tz = get_option('timezone_string');
-	date_default_timezone_set( $tz );
+	if ( !empty( $tz ) )
+		date_default_timezone_set( $tz );
 	$datetime = new DateTime( $string );
 	$datetime->setTimezone( new DateTimeZone('UTC') );
 	$offset = $datetime->getOffset();