Is clearglobalvars=no really working in asterisk 1.2.1?

i am using asterisk 1.2.1 and i tried to work with
clearglobalvars=no in extensions.conf

When i set a global variable with SetGlobalVar() in the dialplan
i expext that this variable is still present after an asterisk restart or a reload command.

But the variable has gone!

Is the clearglobalvars=no feature really working?
Does it depend on other settings like static=no?
Do i have to load special modules to use this feature?