There is an airline in the region that has a similar policy, for foreign pilots only though. They believe they can change, and do, your days off at anytime as they see fit. This includes changing completed duties from STBY to OFF, "because we didn't core you so you were wested."
When asked to explain how come I required to have 10hrs rest after STBY, because it is counted as Duty?
"because we didn't core you so you were wested."
Obviously the regulator will come down on the side of the airline, until there is an accident.
If the flying public understood (not just knew, but understood) some of the stuff airline management do and get away with, they would never step foot on an aircraft again.