Download link missing when check out from GLOBAL SHOPPING CART

Checking out from GLOBAL SHOPPING CART will miss the download link when buying a download-file product from child blogs.

For example, buy this: http://tagtickle.com/tpe48/store/products/%E5%89%8D%E7%94%B0%E6%B5%B7%E5%A0%B1/

and check out in main blog's global cart:
http://tagtickle.com/store/shopping-cart/

It will display no download link in the last confirmation page.

By the way, is it possible to show a FREE icon or words when product setting on $0.00;
also, is it not possible to set on sale price at $0 when the product has original price at above $0?

MarketPress is an excellent plugin, I would like to use all plugin which is from WPMU, so I don't want to switch my Market solution to JigoShop...

so, please help me for my problem... Thanks!