Here are some relevant pieces of the debug log
2014-12-18 14:06:41 934.870 4004 NXSERVER checkLocalSession: Found socket for display [0] – [unix 2 [ ACC ] STREAM LISTENING 17659 @/tmp/.X11-unix/X0]
2014-12-18 14:06:41 935.030 4004 NXSERVER Going to find X server for display: [0]
2014-12-18 14:06:41 935.612 4004 NXSERVER Found X server process: [Xorg.bin /usr/libexec/Xorg.bin :0 -background none -noreset -verbose 3 -logfile /dev/null -auth /run/gdm/auth-for-gdm-WT4O6X/database -seat seat0 -nolisten tcp vt1]
2014-12-18 14:06:41 935.823 4004 NXSERVER checkLocalSession: Found authority /run/gdm/auth-for-gdm-WT4O6X/database.
2014-12-18 14:06:41 935.988 4004 NXSERVER checkLocalSession: Found seat seat0.
2014-12-18 14:06:41 936.290 4004 NXSERVER Found node assigned to display 0.
2014-12-18 14:06:41 936.609 4004 NXSERVER Session for display 0 not changed. Skip recognition.
2014-12-18 14:06:41 936.819 4004 NXSERVER recognizeXSession: kind [session] based on command [mate-session mate-session] pid [1507]
2014-12-18 14:06:41 937.283 4004 NXSERVER checkLocalSession: Found socket for display [1001] – [unix 2 [ ACC ] STREAM LISTENING 41507 /tmp/.X11-unix/X1001]
2014-12-18 14:06:41 937.446 4004 NXSERVER Going to find X server for display: [1001]
2014-12-18 14:06:41 938.330 4004 NXSERVER checkLocalSession: Found socket for display [1001] – [unix 2 [ ACC ] STREAM LISTENING 41506 @/tmp/.X11-unix/X1001]
2014-12-18 14:06:41 938.487 4004 NXSERVER Going to find X server for display: [1001]
2014-12-18 14:06:41 939.473 4004 NXSERVER Found node assigned to session pid 1507.
2014-12-18 14:06:41 939.757 4004 NXSERVER NXPL was already loaded.
2014-12-18 14:06:41 939.919 4004 NXSERVER NXPL::NXGetRandomString start.
2014-12-18 14:06:41 940.071 4004 NXSERVER NXPL::NXGetRandomString stop.
2014-12-18 14:06:41 940.291 4004 NXSERVER isLoginWindowByNXPL random string: 61F8ABE74EE2E298C32BF4DBB733AD24
2014-12-18 14:06:41 940.489 4004 NXSERVER isLoginWindowByNXPL tempfile: /var/NX/nx/.nx/61F8ABE74EE2E298C32BF4DBB733AD24.lcookie_2
2014-12-18 14:06:41 940.971 4004 NXSERVER isLoginWindowByNXPL addCookie(/var/NX/nx/.nx/61F8ABE74EE2E298C32BF4DBB733AD24.lcookie_2, :0, MIT-MAGIC-COOKIE-1, ********) return 0
2014-12-18 14:06:41 941.206 4004 NXSERVER isLoginWindowByNXPL set XAUTHORITY to /var/NX/nx/.nx/61F8ABE74EE2E298C32BF4DBB733AD24.lcookie_2
2014-12-18 14:06:41 941.379 4004 NXSERVER isWMRunningByDisplay call on :0
2014-12-18 14:06:41 942.891 4004 NXSERVER NXPL::NXWmRunning(:0) [1]
2014-12-18 14:06:41 943.067 4004 NXSERVER isLoginWindowByNXPL isWMRunningByDisplay return [1]
2014-12-18 14:06:41 943.301 4004 NXSERVER isLoginWindowByNXPL clean out file: /var/NX/nx/.nx/61F8ABE74EE2E298C32BF4DBB733AD24.lcookie_2
2014-12-18 14:06:41 943.572 4004 NXSERVER isLoginWindowByNXPL(0, ********) return [1]
2014-12-18 14:06:41 943.797 4004 NXSERVER PhysicSessions::isLoginWindowByCK missed all checkpoints