Lutz, your report is not necessary a dupe of the issue which many people face in Xubuntu 14.04. However, you are using components of Xfce 4.11 (PPA) according to the bug description, so it is not a default 12.04 installation anymore and the cause for the problem might be indeed the same.
All comments added to this report thus far address the "new" problem, but feel free to remove the duplicate status and add a note to the bug description to redirect users accordingly.
Lutz, your report is not necessary a dupe of the issue which many people face in Xubuntu 14.04. However, you are using components of Xfce 4.11 (PPA) according to the bug description, so it is not a default 12.04 installation anymore and the cause for the problem might be indeed the same.
All comments added to this report thus far address the "new" problem, but feel free to remove the duplicate status and add a note to the bug description to redirect users accordingly.