currencies keep getting mixed up

hi. we have been using the multi-currency plug in since the beginning of the year and generally it is great. However we do keep getting a strange glitch. Sometimes a customer in USA will get charged in USD but the actual amount is the GBP value. for example the product is set up as £99.99 and $129.99. Normally it is all ok but sometimes a customer will get charged $99.99. -it seems to mix up the value and the currency. This happens both ways, and also with Euro and AUD.

This sometimes also happens when I am manually adding a product to an account. I maybe in the UK product, but when it appears on the customer account is is £129.99 (instead of £99.99), so I have to overwrite the value to be correct. I have checked all the products and each one has the correct values.

This is probably happening about 5-10% of occasions and we can’t work out what is wrong.

Also, maybe related but occasionally a customer will get the order acknowledgement in French when they have purchased the UK/USA product.

thanks for your help.