When two instances of okular are started at the same time, they
hang.

To reproduce (most of the time), do the following (from a konsole
under KDE, in case this makes a difference):

okular /usr/share/doc/quilt/quilt.pdf & okular /usr/share/doc/quilt/quilt.pdf

(You can use any PDF file instead.)

This usually results in two stuck okular processes.

Even starting another one from a different place will hang now.

After "killall okular" everything's back to normal.

This did not happen under previous versions (such as the one in
wheezy).