I tried to compare the strace of the process on both Ubuntu and Lubuntu, which was not feasible due to a very different set of Libraries under Ubuntu (gnome) and Lubunt (Qt).
In order to neutralize these differences I started libreoffice with the environment variables completely wiped (except vor PATH and DISPLAY) and the bug does not occur.
So the problem is somehow caused by different environment variables.
Some progress:
I tried to compare the strace of the process on both Ubuntu and Lubuntu, which was not feasible due to a very different set of Libraries under Ubuntu (gnome) and Lubunt (Qt).
In order to neutralize these differences I started libreoffice with the environment variables completely wiped (except vor PATH and DISPLAY) and the bug does not occur.
So the problem is somehow caused by different environment variables.