I was puzzled by this strange behaviour too. Honestly, after NextGenGallery was sold, it's not getting better.
I did some digging and testing. Turned out, it's function get_date_time() in meta.php (wp-content/plugins/nextgen-gallery/lib/meta.php).
This particular function tries to find image creation date by looping through several EXIF fields. It's all right and proper, but what does it do then? Calls this function on line 522 (that's approximate location, for my version of plugin):
// Return the MySQL format
$date_time = date( 'Y-m-d H:i:s', $date_time );
I really wonder what kind of conversion that was meant to be. Second argument of "date" function was always epoch seconds - and here it gets "normal" Y-M-D H:M:S value. Of course it gets converted into 1970 date. No wonder.
After I commented out that line, everything started working as it should. Hope it will save someone the frustration.