Account for ISO Date timezone indicator

include/class.format.php

@@ -684,6 +684,8 @@ class Format {
             $tz = $datetime->getTimezone()->getName();
             if ($tz && $tz[0] == '+' || $tz[0] == '-')
                 $tz = (int) $datetime->format('Z');
+            elseif ($tz == 'Z')
+                $tz = 'UTC';
             $timezone =  new DateTimeZone(Format::timezone($tz) ?: 'UTC');
             $datetime->setTimezone($timezone);
         } catch (Exception $ex) {