Question: How to reference and evaluate the equation when it contains variables modified by using assume

I am not sure if this is a general problem.  And I am considering the best way to evaluate the expression (Equation) when it contains variables which have been modified by using assume.   Here is a tiny test example:

restart;
assume(a>0,x>0);
int(int(x^2/y^2,y=1/x..x),x=1..a);S:=%:  
                        1  4   1   1  2
                        - a  + - - - a
                        4      4   2   
T:=(1):  #(1) is inserted by using Ctrl+L, which references the first output.
subs(a=2,(1));
                        1  4   1   1  2
                        - a  + - - - a
                        4      4   2   
subs(a=2,S);
                               9
                               -
                               4
subs(a=2,T);
                        1  4   1   1  2
                        - a  + - - - a
                        4      4   2   
int(int(x^2/y^2,y=1/x..x),x=1..a);
                        1  4   1   1  2
                        - a  + - - - a
                        4      4   2   
subs(a=2,%);
                               9
                               -
                               4
subs(`a~`=2,(1));
                               9
                               -
                               4

And you can go through the source file below.

test.pdf

My problem is: Why I can not get the desired result when using Ctrl+L +EquationLabels, if just type subs(Variable=Value, Expression), where Expression has the Variable which has been constrained by ASSUME.