Zen Cart 1.5.5d vanilla install

Option name "Color" and "Size" changed from dropdown to checkbox.

Inserted new product, set "Product Priced by Attributes" to YES. Product price is set to 0.

Going to Attribute Controller. Assigned "Size: Large". Then, new attribute as follows:
Color: Black, price +15, price factor 5, Default Selected YES
Color: Red, price +15, price factor 5, Default Selected YES



Frontend is fine, product info page:



Adding to cart, subtotal is $180 and I go through checkout with $180.

Now, problem.

I go to Price Manager for that product and set a Special Price to 33.33%



Product page is fine and I add the item to cart. Subtotal is $120.



I start checkout, get to checkout_payment page and my subtotal is now $170.



What happened, where is that subtotal coming from? It's not the regular price (that would be $180) and it's not the discounted price (that should be $120 as shown on shopping cart page). Shopping cart sidebox is still showing the correct $120. If I go through checkout, I'm charged $170 (tested on a live site with auth.net and PayPal). Any help would be appreciated.
And, yes, price factor is important because in reality, this is a "bundle" where color:red stands for 6 individual items and we want to show the "per item" price, which is in this case $15 ($10 when discounted). What's most confusing is that shopping_cart page is showing the correct subtotal so that part is working fine...