My friend went through one major usability problem. When signing up, his e-mail address was not correct and could not get the confirmation e-mail, so he needed to fill the form again, but he kept getting the "Next step check your e-mail address. You can close this tab...." popup. It took him a long time to figure out he has to reload the page to get the sign up form.
So I would rectify this whether by not reloading the "Netx step...." popup after the user closed it or by adding "Please reload the page to get the sign up form" in the popup