Strange behaviour with shippingcosts

[Sven Franke]

Hi,

When I place an order, the payment includes the shippingcost nicely. The customer gets to pay the correct amount. But on the invoice there are no shipping costs (free shipping). Also, when I go to the dashboard, it show the amount without shipping costs and there is a warning that the customer paid to much. 

I've read about this issue more in the forum, but no clear solution. The strange thing is, that the correct amount was calculated at pay time, so what happend?

I'm using PS 1.7.6.3. with the Sisow payment module (that seems to work correct, because the customer paid the correct amount).

Anybody with a proper solution?

Sven.