I start vnc4server in Debian Jessie using command line below:
vncserver :1
The part of ~/.vnc/xstartup as below:
#************
export GTK_IM_MODULE=xim
export QT_IM_MODULE=xim
export XMODIFIERS=@im=fcitx
fcitx &
gnome-session &
#************

I can't activated fcitx in vncviewer remotely with any keys combination,
I have changed the different keys combination for activating input method
in the guest machine.

The "xstartup" configuration has been used in Debian 6 normally.

Fcitx still can't work in vnc environment of Debian 7 normally, but act
the other strange behavior, I will report it in my Debian 7 machine soon.

Ibus has no this kind of broblem.