Rates in a steady turn.
In any practical, stable, banked turn, the aircraft will have roll, yaw and pitch rates simultaneously, even though the bank angle and pitch attitude will be fixed and it appears that the only attitude angle change is in heading.
This is because the roll, yaw and pitch rates are defined in an axis system which is fixed in the aircraft, and the bank angle, pitch attitude and heading (yaw attitude) are all defined by the relationship of that aircraft-fixed axis system to the earth-axis system.
The trick is that rate of change of bank angle is NOT mathematically the same as roll rate; nor for the other axes. Those are approximations which hold good for a given level of accuracy, but not to the ultimate.
If you had no angle of attack, such that the aircraft x-axis - about which we measure roll rate - was perfectly aligned with the velocity vector, you'd have no roll rate, but that's all. You'd still have a yaw rate and a pitch rate.
Having spent many happy hours explaining that, no, the simulator is working properly, those rates on the IRU are REAL, down to digging out the relevant equations of motion, I'm pretty sure of that lot.