Payment Error due to difference in total amount between frontend and backend

[CB Bear]

Almost a month using Prestashop, using Dutch iDeal payment system.

The current version is 1.5.6.2.

 

Problem:

In case of some orders something seems to go wrong when totalising the final amount.

In about 70% of the orders everything has been ok.

 

But in many cases something has gone wrong at the end, when processing the payment.

In the order list this is indicated by "Payment Error".

When viewing this, the amount that was substracted from the bank account was just 1 or 2 cent more than the total in the Shopping cart. So there was a difference between the total ammount and the amount cashed.

 

No payment was recorded for the order history, but the money was cashed from the bankaccount. Also than no invoice is automatically generated.

 

The customer receives a notofication that something has gone wrong with the order payment.

 

So, what makes it happens that in most cases the order goes well and in other cases not.

Does it has anything to do with the amount rounding? Why is then the front end not equal with the back end amount. Is something here configurable?

 

Who can help me.  Thanks in adavance.