The retail store we've created has numerous products with different sizes, which we've set up as child products to the main products. They show as options in a dropdown and selecting any option first tie through and adding to cart works fine. But after selecting each one (without leaving the product) and seeing the qty/prices change just fine, upon going back again and selecting a previous option, the prices do not change. Even though the options box shows the correct selection, the price of the last previous option (first time through) you've selected is used in the add to cart, not the one you actually want. This only occurs when selecting each option to see which options are available but then returning to a previous option as the one you want. The first time through if you add to cart one of the options the correct pricing shows and is added to the cart properly. Second time through, no. See: https://elliottsfinenutrition.com/store/2073/raw-prenatal-detail as an example of one such product.
Using Joomla 3.5.1 with VirtueMart 3.0.16, PHP Version 5.4.45 on an active site operating for several years, with only this year implementing the options/variants. Prior to combining, had them as separate products.
http://forum.virtuemart.net/index.php?topic=79799.0