Grade Ladder progression

I created progression grade ladder and linked it with the created grades.
I linked the salary basis with this progression grade ladder.
In the employment form I linked the employee with grade ladder and grade step, I choose grade step A.
In change salary form I created salary line, the value of the salary came automatic from the grade step rate, which is true.
When I made change in the employment form by change the grade step from A to B and go salary change and tried to enter new line for the new grade step, I found the value