This bug always happens no matter what launch vehicle you use. If you print the ratio of the current mass flow rate and the maximum mass flow rate of an engine with respect to the throttle you can see that there is a difference between them. Although this value is very small (in the millionth of a percentage), this makes it extremly hard to fine tune trajectories due to this small difference.
The ratio bewteen current mass flow rate and maximum mass flow rate with the throttle value is not the same.
1.8 years ago
Such small difference is likely to be due to floating point precision or the use of a float instead of a double somewhere, it shouldn't have any noticeable effects on what you are trying to do.