There's no cart if you view your items from the US site, just tried it. 
Looks like it's all Australian sellers' items.... (just checked my own).
That's madness. 
Sorry, I can't offer a solution but this started happening to some Oz sellers in a particular category (trading cards) several months ago, and I can't believe that not only has the problem not been fixed, it's expanded. ๐ (Reason given back then was that buyers were opening INR or INAD cases on all purchased items if only one in their lot was missing, damaged or faulty, so making them checkout individually was eBay's "solution").
It's particularly bad now that FVF is being charged on postage here (and, unlike in the US where it's only charged on the first domestic option, it's on whatever is charged to the buyer when they checkout), and there is no FVF credit if you refund overages.
eBay, the timing for this glitch / update / whatever is not making you look very good. 
This is the thread where the issue was first brought to light, http://community.ebay.com.au/t5/Selling/Selling-to-the-USA-and-UK-Buyers-are-having-to-pay-for-each/...
starting January and continued denial of the problem by ebay, then there was an acknowledgement of a "tech issue" with a promise they were working on it, then one of the sellers was informed it was a deliberate change.
The only workarounds we could come up with is either advising OS buyers to log into eBay AU so that they can use the cart and/or BIN items individually, or by offering an alternative payment method that - while doesn't make the Add to Cart button available on OS sites - means that if a buyer selects it when they are directed to pay immediately, they can instead commit to purchase like a normal BIN. Neither of which are particularly elegant or intuitive solutions, and really doesn't address the problem at large. ๐
I think this problem needs more attention, because it basically means eBay are effectively all but forcing immediate payment required on all Australian listings for buyers located overseas, as well as removing the ability for even automatic postage dicounts to come into effect by disabling the cart for Oz listings on OS sites, meaning that the maximum amount of FVF is levied on each individual item, and that's just wrong.
