This one will need to go to Steve Brady (FocusMax author). ACP explicitly sets "return to start position" to True before every call to focus. Did this "just start happening"? Look for clues.

        ' Regardless whether we use AcquireStar or our star selector,
        ' we need FM to return to prev focus if there is a focus failure.
        c_FMx.FocusRoutineReturnToStartPositionEnable = True