dead end when changing user

[Jürgen]

one user is logged in
after resume another person wants to log in
there are options
<old user>
<unused>

choosing new sesssion end up in a loggin window for the first user (with two overlapping buttons underneath)

using <strg><alt><f1> .. <f7> doesn't appear to change anything but if you type blind
(<Alt><F1> .. <Login> .. shutdown -r 0
I could reboot the computer.

Whenever this happens one option is to log in (if you have the password) and log this user out. Interesting is that you cannot <Alt><F1> within that session anymore.

After loggin out everything seems to be normal again.

We have sometimes up to three concurrent sessions and maybe it is related to the sequence how the users log out again leaving for example only the last user <Alt> <F9> active.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: lightdm 1.8.4-0ubuntu1
ProcVersionSignature: Ubuntu 3.11.0-14.21-generic 3.11.7
Uname: Linux 3.11.0-14-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.12.5-0ubuntu2.1
Architecture: amd64
Date: Sat Dec 14 10:45:02 2013
MarkForUpload: True
SourcePackage: lightdm
UpgradeStatus: Upgraded to saucy on 2013-10-20 (54 days ago)

[Gold Star (goldstar611)]

I have had the overlapping buttons happen to me as well. Very difficult to recover from less a CPU reset