One little thing still occurs ...
When the customer clicks the back-button after he confirmed (on confirmed page) and submits the checkout page again, he will be redirected to the page from the "eCart Redirect If Empty" behaviour. No mail will be sent, that's ok.
Also there is no record added in the database, although the orderID-number of the following order increases with two.
Most likely is it due to "eCart Store Cart Summary (& Details) in Db" !?
Is there a way to prevent this ?