Android: get wrong HorizontalScrollOffset when a RecyclerView inside ListView is scrolled to end

Question

Can anyone tell why, a Horizontal RecyclerView inside a ListView return wrong computeHorizontalScrollOffset() when it is scrolled to end?

I set a holder.recyclerView.addOnScrollListener() in my ListView adapter, getView() like this:

@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
    super.onScrollStateChanged(recyclerView, newState);

    if (newState == RecyclerView.SCROLL_STATE_IDLE) {
        float horizontalScrollOffSet = recyclerView.computeHorizontalScrollOffset();
        int expectedPosition = Math.round((horizontalScrollOffSet + padding - firstItemWidth) / itemWidth);

        Log.i("position", "horizontalScrollOffSet:"+horizontalScrollOffSet+",expectedPosition:"+expectedPosition);
    }

}

The Log.i data:

The offset figures are supposed to be increasing while the view is scrolled from left to right, everything works fine except when it's scrolled to the end, it just returned a smaller figure. I really have no idea about this but I need it to compute the items' center points. Can anyone please guide? :'(

From what I tried out, the RecyclerView works fine when last padding item size is set to the same as main item size.