I checked the whole newspaper this morning and have to say that I was wrong in the matter that every article would be affected. In fact, some work, some don't. Even in the same feed. Here an example of today's delivery, feed=Vermischtes :
no vorspann :
http://www.noz.de/deutschland-und-we...tz-von-helfern
with vorspann :
http://www.noz.de/deutschland-und-we...t-kinobesucher
I was not able to find any remarkable difference in the "enlargeable vorspann" tag. Maybe the problem occurs somewhere in a step before that.