Tax error at checkout

I have two product types, one set as taxable, the other not.

If I have only the non-taxable product in my shopping cart, no tax is applied at the checkout, which is correct.

If I have only the taxable product in my my shopping cart, tax is applied at the checkout, which is also correct.

However, if I have both taxable and non-taxable products in my shopping cart, tax is applied to all products at checkout, which is wrong.