Mesa Mark V:35 help

So I just bought a Mark V:35 head, and I’m seeing something strange and want to know if something is wrong with my amp.

The thing that I’m wondering if it’s a problem / mod someone did is that when I’m using the clean channel, on the Fat and Clean settings, the gain controls total volume and the Master volume does nothing. I’m not seeing anything in the manual and nothing in my web searches. The Solo Master volume works, and the Master knob on channel 1 also works for the Crunch setting. It’s just strange that it doesn’t do anything for the Clean/Fat settings. Anybody have any experience with this amp and can lend a hand?