I tried your preset again. I dimed Master Volume and Amp Level. The result was, of course, extremely loud. Between the Master Volume and the Amp Level, you're adding about 40 dB to the signal. That's the difference between 1 watt and 10,000 watts! Everything from the Amp block to the output was clipping. And yes, there was enough level to come through even when the volume knob was all the way down. Not surprising, when your signal is 10,000 times hotter.
At that point, I switched to Dyna-Cab mode, and the result was the same. In either case, behavior returned to normal when I reduced Level and Master Volume to reasonable levels.
Curiously, though, the output CLIP LEDs never lit, even though the meters showed clipping in most of the signal chain.
@rglr?