Wrong SKU on Product Detail page, if Product has Up-Sell items

[sneader]

When viewing the details page of a product, if that product has Up-Sell items listed, the SKU of the product being viewed will show the last Up-Sell item's SKU.

Example:

Product A has SKU of 123
Product B has SKU of 456
Product C has SKU of 789

When viewing Product A, without any up-sell items, the SKU will display correctly as 123.

If you make Product B an "Up-Sell" item on Product A... then when you view Product A, the SKU will display 456 (wrong!)

If you also make Product C an Up-Sell item on Product A... then when you view Product A, the SKU will display 489 (wrong!)