Problem cart and products with sizes

[icaro76]

hello
Use the version of 2.0.10 and joomla virtuemart 2.5.7 I am preparing product sheets and some products include the cuts and colors I set everything with custom fields using the plug in just for insert sizes, I have set as a variant of the trolley now this happens to me every time I select the size it automatically adds to cart, even if I try to store all the various sizes and the add to cart button, I would like to understand what is happening, how do i select the product do not automatically add in the basket? someone can help me?
It is normal for a custom field used as a variant of the truck replace the add to cart button?