To reproduce this step:
1) add a product to cart (you MUST be unlogged!)
2) hit the "Continue with order" button: you are correctly redirected to the login/register form page....
3) now try to go back to the cart ( http://<web-site-url>/index.php?option=com_virtuemart&view=cart )
4) you are redirected again to the login/register form: this is wrong, you must go back to your cart as requested (and there eventually choose again to continue with order -> login/subscribe)
Fixed, thank you