So, I wasn't sure if this was just a version problem or something (using EE 2.7 and Store 1.6.4 - the latest).
When I try to add items to my cart, they aren't successfully added and the network inspector shows that the POST is being 302 redirected to a GET. I tried a variety of htaccess setups, including not having one at all putting the index.php back into the URL. Nothing seems to work.
Here's the POST data:
ACT 41 RET products/my-product-page XID 32e30b64c0bdc8d9c5912d91c3764ad4b3c194b4 _params JklZbhzeb7aea+I4IB82StmfY1Bt/4jVC9XT2EbcV+2jeMX3Q7EKeZa1LWwiLh8f59h6n8Xsuaz6Rw0guwFpEcECKeZgLN+OS3uk8QTCaXfx0p5UR+jTgFl0uB/QVDedMkUuXXpki2aPaFrUgy3UT4unGSK+juDkn+zDQUrKRWqVjoHVguKqoxKI2LuFQJPELKTP0tPbhBFdXSYMUYw1213qV8VMWQPV4XKLmuTMyt4YprL/Kh8jy3AkiNaOem8JaClZfaunEZlM+ehf+9FG8SyzwmsRm4SefiwhY8V2wHI= entry_id 40 item_qty 1 modifiers_3 10 return_url store/checkout site_id 1 submit Add to Cart
The URL for both the POST and GET are exactly the same. No differing slashes or anything. Using PHP 5.3.22 and Apache.