Thus far, my experiences with Acting Pay have been different. I have seen:
1. Retro acting pay put on a separate payment, where pension contributions were deducted, but the retro pay not paid out.
2. Acting pay at the base rate of the higher classification for the acting period, which is less than the substantive rate of pay. Or, in other words, do the job of the boss and take a pay cut.
3. Acting pay at a higher rate of pay that does not exist anywhere on the pay table, because they are applying the 4% rule instead of the "next higher incentive with a minimum increase" rule.
Of course, pay statements don't show your annual rate of pay, so if you're not conversant with the conversion factor from biweekly to annual, you may not notice that your pay rate is wrong.