When saving my responses in order to answer the survey at a later time, the saved_date field in saved_control table is always valorized with 1970-01-01 01:00:00.
On the other hand all dates (submitdate,startdate,datestamp) are correctly valorized in the survey table.

Concerning my installation, the problem seems to be connected to the instruction "$today = dateShift(date("Y-m-d H:i:s"), "Y-m-d H:i:s", $timeadjust);" in application\libraries\Save.php line 167, where the variable $timeadjust is not correctly valorized.
If I modify the above mentioned file, i.e. by setting the variable $timeadjust = "+1 hours", then the saved_date field in saved_control table is correctly valorized.