They are creatively rerouting line holders as well as reservists with no regard for the contract. I've had 3 in the last month and they tried to not pay me for all 3. The 1st they were legal to not pay extra, the 2nd one I challenged earned me and the captain 2 hours of straight pay, and the 3rd I challenged earned me over 8 hours of reroute pay. Be a squeaky wheel and don't accept when they violate the contract. The more they violate the contract and get away with it, the more they will violate the contract.

edit: btw, just to clarify all 3 of my reroutes were legal. They just tried to screw me out of pay while doing it. I've never been in your position cap'n but it sounds fishy. I'd definitely follow-up if I were you. My gut says you should at least get the same kind of PB you'd get if you were GSing on an XX day.