I changed function "wpcf7_the_post" in contact-form-7/includes/controller.php to this:
function wpcf7_the_post() {
global $wpcf7;
if(count( (array)$wpcf7) == 0)
$wpcf7 = new stdClass();
$wpcf7->processing_within = 'p' . get_the_ID();
$wpcf7->unit_count = 0;
}
It's not a big issue but hope authors will fix it soon.