Log out of VM portal only works at the second try

Issue

• A user logs in to the VM portal, starts a VM and logs out. So, the screen with the selection "Administration Portal, User Portal, Downloads... " reappears. User seems to be logged out, but when the user selects the User Portal again, no login screen appears. The user directly sees the VMs without entering user / password. When the user logs out for the second time it is successful. After selecting the User Portal again he has to log in as expected.