@vlad59 & @le_
I can confirm the possible bug (regression).
It seems as if the lightbox (Magnific Popup) cannot be "nested". In version 4 of COPS it worked with Fancybox. Did not test COPS 5.
..... so it seems you have watched to many episodes of "The IT Crowd"

there should be one final episode later in 2013.
Source
http://www.bbc.co.uk/news/entertainment-arts-22449971
Looking forward to that!