Index: uc_discount.module
===================================================================
--- uc_discount.module	(revision 357)
+++ uc_discount.module	(working copy)
@@ -109,6 +109,19 @@
       $node = clone $context['subject']['node'];
       $cache = 'node:'. $node->nid .':'. $price_info['price'];
       break;
+    case 'attribute_option':
+      // If there is no node in the $context, we are either on the node's 
+      // attributes admin page or in product classes attributes, and in both 
+      // cases should show no discount.
+      if (!isset($context['subject']['node'])) {
+        return;
+      }
+      $node = clone $context['subject']['node'];
+      $cache = implode(':', array('node', $node->nid, 'attribute_option', $context['subject']['option']->oid));
+      // We only pass a $node to the action, so hack into this a property so the action
+      // knows it's working on an attribute option price.
+      $node->uc_discount_attribute_option = $context['subject']['option']->oid;
+      break;  
     case 'cart_item':
       $node = clone $context['subject']['node'];
       $item = $context['subject']['cart_item'];
Index: uc_discount.ca.inc
===================================================================
--- uc_discount.ca.inc	(revision 357)
+++ uc_discount.ca.inc	(working copy)
@@ -400,6 +399,15 @@
  * @see uc_discount_ca_action()
  */
 function uc_discount_get_discount($entity, $settings) {
+  // Retrieve our hacked-in flag from the product. This lets us know that we're
+  // altering an attribute option price rather than the base price. These
+  // should only be affected by 'multiply' discounts and not 'add'.
+  if (isset($entity->uc_discount_attribute_option)) {
+    if ($settings['operation'] == 'add') {
+      return 0; 
+    }
+  }
+
   // If we are adding a base number as a discount, return it.
   if ($settings['operation'] == 'add') {
     return floatval($settings['amount']);