Page scrolls on magnific popup

Hi there. Please take a look at the page in the “private content”. I used the method described in this post…

https://kriesi.at/support/topic/menu-link-to-open-content-in-new-lightbox-magnific-popup/

…to create a menu link that triggers the popup of a login form div. Works like a charm except when I click the “Login Test” link in the main menu, the page scrolls down a couple inches. When I close the popup, the page flashed back to the top. How can I prevent this scrolling?

Thanks!