Overriding Rates on Future reservations after a Rate Increase

After making a $5.00 rate increase in our system - we are now noticing future reservations that have over-ridden rates - subsequently deleting the rate code WHICH NEEDS TO REMAIN. This system seems to take every opportunity to wipe out a rate code and we have to figure out how to get it back in there again. Now we have to go into all those reservations and fix them with the discount function. ONCE A RESERVATION IS MADE - LEAVE IT ALONE UNLESS IT IS MANUALLY CHANGED BY THE PROPERTY. I don't understand why you would mess with a reservation for the future - just because it was made prior to a rate change. Frustrating.