I found a mismatch related to the valid range of ACRO_Y_EXPO parameter.
ACRO_Y_EXPO’s valid range is from -0.5 to 1.0 based on documentation. However, ArduPilot source code forces the parameter to have a value from 0 to 1.
g2.acro_y_expo = constrain_float(g2.acro_y_expo, 0.0f, 1.0f);
in ArduCopter/mode.cpp 753 line
I think this issue is similar to #3541.