Var into an external swf

I declared a var into a MC like:
var x1:int=5;

I load this Mc into anoteher MovieClip, and once it’s loaded, i try to call the var x1, and i found the var, but not it’s value :
trace(mc.x1) // gives 0, not 5

So where’s the mistake, it can find that x1 is a int, (if i try to trace a non exist value, like x2 i get “undefined”) but it cannot find it’s value, how is it possible ?