Verifique se o diretório pessoal do usuário é adequado e se possui as permissões necessárias. Eu enfrento um problema semelhante ao adicionar um novo usuário no Debian.
Estou executando uma nova instalação do Debian Jessie e apenas tentei instalar o KDE e quando eu logro escolhendo plasma como meu ambiente de desktop ele vai para uma tela de plasma por alguns segundos e então volta para a tela de login normal. Como posso consertar isso? Onde você olharia?
O conteúdo do meu arquivo .xsession-errors é o seguinte:
Xsession: X session started for nathan at Thu Oct 29 00:56:25 MDT 2015
localuser:nathan being added to access control list
Loading stage "initial" 193
startkde: Starting up...
kdeinit5: preparing to launch 'libkdeinit5_klauncher'
kdeinit5: Launched KLauncher, pid = 950, result = 0
Qt: Session management error: networkIdsList argument is NULL
Connecting to deprecated signal QDBusConnectionInterface::serviceOwnerChanged(QString,QString,QString)
kdeinit5: opened connection to :1
kdeinit5: preparing to launch 'libkdeinit5_kded5'
kdeinit5: Launched KDED, pid = 952 result = 0
kdeinit5: preparing to launch 'libkdeinit5_kcminit_startup'
kdeinit5: Launched 'kcminit_startup', pid = 953 result = 0
Qt: Session management error: networkIdsList argument is NULL
Recreating ksycoca file ("/home/nathan/.cache /ksycoca5_en_ABGG1sD7FGwLWpevNW74RXeZhv0=", version 303)
KCrash: crashing... crashRecursionCounter = 2
KCrash: Application Name = kdeinit5 path = /usr/bin pid = 952
KCrash: Arguments: /usr/bin/kdeinit5
KCrash: Attempting to start /usr/lib/x86_64-linux-gnu/libexec/drkonqi from kdeinit
kdeinit5: Got EXEC_NEW '/usr/lib/x86_64-linux-gnu/libexec/drkonqi' from wrapper.
kdeinit5: preparing to launch '/usr/lib/x86_64-linux-gnu/libexec/drkonqi'
kdeinit5: PID 957 terminated.
Menu "applications-kmenuedit.menu" not found.
Saving
kdeinit5: Got SETENV 'KDE_MULTIHEAD=false' from launcher.
Initializing "kcm_input" : "kcminit_mouse"
kdeinit5: PID 953 terminated.
KCrash: crashing... crashRecursionCounter = 2
KCrash: Application Name = kdeinit5 path = /usr/bin pid = 954
KCrash: Arguments: /usr/bin/kdeinit5
KCrash: Attempting to start /usr/lib/x86_64-linux-gnu/libexec/drkonqi from kdeinit
kdeinit5: Got EXEC_NEW '/usr/lib/x86_64-linux-gnu/libexec/drkonqi' from wrapper.
kdeinit5: preparing to launch '/usr/lib/x86_64-linux-gnu/libexec/drkonqi'
kdeinit5: Got KWRAPPER 'ksmserver' from wrapper.
kdeinit5: preparing to launch 'libkdeinit5_ksmserver'
kdeinit5: PID 952 terminated.
kdeinit5: PID 960 terminated.
Qt: Session management error: networkIdsList argument is NULL
KCrash: crashing... crashRecursionCounter = 2
KCrash: Application Name = kdeinit5 path = /usr/bin pid = 961
KCrash: Arguments: /usr/bin/kdeinit5
KCrash: Attempting to start /usr/lib/x86_64-linux-gnu/libexec/drkonqi from kdeinit
kdeinit5: Got EXEC_NEW '/usr/lib/x86_64-linux-gnu/libexec/drkonqi' from wrapper.
kdeinit5: preparing to launch '/usr/lib/x86_64-linux-gnu/libexec/drkonqi'
kdeinit5: PID 964 terminated.
kdeinit5: PID 961 terminated.
startkde: Shutting down...
kdeinit5: terminate KDE.
klauncher: Exiting on signal 1
startkde: Running shutdown scripts...
startkde: Done.
Verifique se o diretório pessoal do usuário é adequado e se possui as permissões necessárias. Eu enfrento um problema semelhante ao adicionar um novo usuário no Debian.