Budget not increasing

Why is it our budget goes down when we make a worker ineligible but it doesn't seem to go back up should we then make them eligible again?

Summary: We have an annual Salary Review which we use a Compensation Plan for. We have noticed when we make a worker ineligible the budget does go down which is what we expect however should we then make the worker eligible again the budget doesn't go back up. Has anyone else experienced this or know a solution? We have tried refreshing plan after the changes but this makes no difference. Is there another process that needs to be run or is there some setting on my plan impacting this?