List of VARs operation

I am sure I have got this expectation totally wrong and need another explanation of why this does not work:

I am trying to create a vector like structure using a list of 2 item var:
x and y are either local or global vars.

After executing the block I get:

Now I want to change the x value:

Result is:

Why is the vLoc list value not changing, unless I rexecute the
image block ?

The list will not be updated unless you have a script like if ((x and y) > 0) set [vLoc v] to (list (x)(y)).

In Snap!, as in almost all programming languages, the expressions that provide inputs to procedures are evaluated before the procedure is called. So when you say list x y, the two input expressions x and y are evaluated before list is called. So list knows only that the values of its inputs are 0 and 0; it has no idea what expressions gave rise to those zeros.