Recently I encountered a problem that my input method malfunctions because the environmental variables are wrongly set(which is, fully configured using im-config), after hours of debugging I found that it's Z-shell(my current default shell)'s bug that prematurely quits before the Xsession.d im-config input method configure script completes. The problem is, /etc/X11/Xsession (and all the Xsession.d scripts it sourced) **shouldn't** be run in Z-shell. Patching /etc/kde4/kdm/Xsession # invoke global X session script. code from . /etc/X11/Xsession to /etc/X11/Xsession workarounded the issue (however I have no idea why). Switching to other display managers instead of KDM worked also) Reproducible: Always Steps to Reproduce: Currently there's no simple reproduce method as another software(zsh)'s bug involved.
Downstream bug report: Bug #1364173 “Xsession sourced scripts shouldn't be run using us...” : Bugs : KDE Base Workspace https://bugs.launchpad.net/kdebase-workspace/+bug/1364173
Here's the Zsh bug report end that Zsh is behave properly, but not the same way as Bash do. Z-Shell breaks im-config configuration scripts, making input method malfunction http://www.zsh.org/mla/workers/2014/msg00886.html
I found out that kdm runs /etc/kde4/kdm/Xsession using user's default shell. http://i.imgur.com/xyiJ1b8.jpg It is not sane as in Xsession(5) manpage notes: /etc/X11/Xsession is a Bourne shell (sh(1)) script which is run when an X Window System session is begun by startx(1) or a display manager such as xdm(1).
KDM is unmaintained and not used in KDE Plasma 5. SDDM is the login manager used in KDE Plasma 5. If you still have this same issue with SDDM, please file an issue on the SDDM bugtracker (after doing a search for existing issues first!): https://github.com/sddm/sddm/issues/