Grade step rate value audit table not populated

We have enabled auditing for the Grade step rate and Grade step. After enabling, while all transactions for Grade step are being recorded in the per_grade_steps_f_ table, when we modify the step rate value through the following navigation:
Progression Grade Ladder -> search for the grade ladder -> go to Grade and step -> update or add a new step and add a new step rate value, the per_rate_values_f_ table is not getting updated.
However, I can see these values in the per_rate_values_f table(non audit table)

Please note that while the per_rate_values_f_ table is being populated for Grade rates, it is not being populated for Grade step rates.