Why is virt-manager running on KDE not showing CD-ROM connect window?

Issue

We use RHEL 6.4 as KVM host and virt-manager to configure the virtual machines. While the host crashed we reinstalled and changed from Gnome to KDE on the test lab host to run the virt-manager locally. Now we have an issue that it is not anymore possible to insert virtual CD-ROM images using virt-manager. When click on the "Connect" button nothing happens.