Checkbox Attributes and Quantities

I am trying to set up an item, for example:

Product "Pirates of the Caribbean", with long description of the story.

With attribute checkboxes

Book
DVD
Music CD

No quantities, just accepting 1 on Add to Cart.

So I tick Book and click Add to cart, and it goes in the cart OK and lists the attribute. That's OK.

Then I go back and tick DVD, click Add to Cart, and it goes in the cart as a second listing. That's OK.

Then I go back and tick Book AND tick Music CD, click Add to Cart.

The problem is that the first shopping cart item quantity is now 2, but the attributes say Book and Music CD. So I don't know whether he wants 2 books or 2 Music CDs.

I am trying to get around this, but would appreciate some help.

It would be OK to list a new shopping cart item for each Add to Cart click, but I don't know where to change that.

Or, better, just allow them 1 checkbox to be clicked at a time before Add to Cart - I did change the attribute listing to have an Add to Cart on each attribute, and hide the checkbox, but I could not work how to automatically tick the checkbox on the button click.

I've been playing around with attributes.php, tpl_product_info_display.php, and tpl_modules_attributes. (My own template versions of.)

Thanks.
(no link online as yet)

Looking at this even more, is this a bug?

I am pricing by attributes, and in the above example, they have ordered 2 x Books and 1 x Music CD, but because they clicked Add to Cart Twice, they are paying for (this is the way it is calculated) 2 x Books and 2 x Music CDs.