Normal coupled LOC approach with A/C heading not matching Selected Course is usually due to crosswind. If you are stabilized on approach, the autopilot has whatever crosswind compensated for. If you then change the CRS, it's like a changing crosswind, appearing to the autopilot it requires a new CRS washout, which it soon learns isn't so, as it's main input is LOC deviation.
Not sure I've explained it concisely.
GB