Sometimes the regulations are stupid cases of "the computer says no".
As a civvie with a freedom to choose I often travel to London for various meetings; I travel 1st Class.
My colleague who works for the local government authority attends the same meeting. He travels 2nd class as that is their rules to save money. My ticket is often 10-15% cheaper than his and I get fed and watered; he claims additional expenses for his meal!
No matter how he protests to his bosses, it just falls on deaf ears.