The code posted in the accepted answer cannot be found in a default Magento install.
Thus I'm pretty sure the issue can be caused by the JavaScript method called reloadPrice
.
Interestingly, when checking the block that renders the attribute dropdown you can find this:
if (!$this->getSkipJsReloadPrice()) {
$extraParams .= ' onchange="opConfig.reloadPrice()"';
}
I'm pretty sure you can set that parameter via layout XML by doing this:
<catalog_product_view>
<reference name="product.info.options">
<action method="setData">
<name>skip_js_reload_price</name>
<value>true</value>
</action>
</referencen>
</catalog_product_view>