This is in no way a bug, but a very common misunderstanding. Let's see what happens when I say
var a = b;
Integers and other javascript primitives, like floats and booleans, are "assigned by value".
Which means that whatever value b has is going to be copied to a. To the computer, it means having the part of memory that b references copied to the memory that a references. That's the behavior you were expecting.
When arrays and other objects (and "descendants" of a new Object() call) are used like that, there is a copy by reference. Meaning that the value of a now references the value of b, the memory that b references isn't copied or modified. Thus, when writing
a = [1,2,3];
b = a;
b and a become interchangeable. They're referencing the same memory address. To achieve what you're trying to do, use
var copy_initial_variable = initial_variable.slice(0);
Read Does JavaScript pass by reference? for more information.
