VAT -0.01 error

I wonder if anyone else is having this problem.

We have recently been seeing some VAT zero-rated products enter -0.01 in the VAT Amount column on sales orders.  There doesn't seem to be a pattern to which products are doing this, except for the fact that they are VAT zero-rated, so the VAT Amount should, of course, be zero.

For example, I put an order on the system this morning.  There were about 20 line items, all VAT zero-rated.  Two of the lines have -0.01 in the VAT amount column, making the total VAT amount on the transaction -0.02.

This is causing us serious problems because when the order gets fulfilled and billed, the error corrects itself.  In the case of web orders, this means we have authorised the lower amount and the credit card release of funds fails because we are trying to take 1 or 2p more than is authorised.  Due to Netsuite's fantastic alerting system when release fails, we have no way of knowing about the failed releases other than trawling through the gateway provider's control panel.  Fun!