Yes, but I think I found the problem, thanks to Axis and Ohs.
When I spawn into a flight at a parking spot, as I am for this one, Axis and Ohs doesn't load the aircraft profile, it loads a profile for "Avatar" -- and as indicated by someone on the MSFS forum, as soon as I enter the plane using shift-C, it stops rolling - presumably because at this point it loads the aircraft profile with the parking brake set.
I did set a binding in the MSFS control settings as well and made sure the brake was set, but I suspect MSFS doesn't load the native profile until you enter the plane either, because it didn't help. So it looks like it's an issue particular to walk-around mode.