Using Prince 7.0 b1 with the index.html from the following ZIP archive:

http://www.immanuel.de/tmp/justification.zip

On the second page the first line of the paragraph with

"""
Über 500 Teilnehmer aus 39 Ländern trafen sich am 15. und 16. Mai 2008 in der Charitée ....
"""

has no proper justification on the first line...

Bug or Feature?

We've just released Prince 7.0 (although the website is not fully updated yet), would you be interested in downloading the latest build and seeing if (hopefully) the problem is already fixed?

Sure, URL?

Ok, found the 7.0 version and re-tried: same issue.

The gap at the end of the line is the empty <div> element with class "image-box", which is floated to the right and has 1em padding taking up space. This gives the appearance of an unjustified line. Try putting a red border on the image-box element to see how it is taking up space.