why Ctrl+Space doesn't work

bingo.xrfu

i have installed fcitx1.8.5 on my Mandrake9.1 linux. At first, Ctrl+space did work, and i could input chinese though i couldnot see anything in the input bar. But after several reinstallations and changes of configuration files(i cannot remember exactly what i have done), it didn't work. Then i tried fcitx 1.8.2 and even xsim, the same problem accured. None of the input methods responsed to Ctrl+space. why? i need your help!!

bingo.xrfu

终于可以输入中文了，但是解决的办法令我感到不解，还请高手指点。我现在用的是xsim。以前一直是只出现“简”字图标，但是ctrl＋space没有任何反应。后来我又再次尝试修改.bashrc文件，将其中的
export XMODIFIERS＝"@im=xsim"
一行改成了
export XMODIFIERS="@im=XSIM"
一切就ok了（注意只有大小写的区别）！ 虽然我知道linux是区分大小写的，但是为什么要用大写呢？我安装和运行xsim都用小写的啊。
估计前面我装fcitx遇到的问题也可以用类似的办法解决，我再试试。

bingo.xrfu

我试了好多次了，对于xsim输入法，用小写Ctrl＋Space就不能用，改成大写就ok了。但是对于fcitx就没办法了，怎么试还是没办法调出输入条来。现在只好用xsim了。

高手指点！！