Problems calculating taxes

Hello.

I have 2 types of taxes, but it doesn’t let me calculate them properly. When I add another tax to the invoice and click “Calculate taxes”, this tax is replaced with one that’s set by default. How can I solve this?

Also (I don’t know if it’s related with this), it doesn’t let me calculate the total properly. It divides the shipping, the taxes and the total amount separately, but it says that the order remaining is less than the total, even when there has been no payment.

Hope you can lend me a hand with this.

Thanks in advance.