I noticed this during the beta as well but wasn’t sure if it was already listed to be fixed.
When utilizing lightboxes, it appears that when clicked it opens in the mini-window and then reloads in the entire browser window. The URL refreshes showing the landingpage.com/unbounceurl /4-lightbox.html and therefore navigating away from the landing page.
I saw this on both Chrome and Internet Explorer on Windows 7. I was able to replicate this on three computers so far in the office computers.
Any help appreciated!