Tableview scroll to top not going all the way

问题:

I have a navigation bar that I've manually coded to animate the frame of depending on the offset of the scrollView (tableView). Below is a screenshot of what it looks like unscrolled.

Now after setScrollOffset:(0,0) is invoked (by scrollsToTop, not me manually - e.g. by tapping status bar), the scrollview scrolls to the top, but at the position at which there used to be no navigation bar. I can manually scroll the last 44px or so after the animation happens, but obviously thats not the behavior that's expected.

Here is my code for hiding the navbar:

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGRect frame = self.navigationController.navigationBar.frame;
    CGFloat size = frame.size.height - kMacro1;
    CGFloat framePercentageHidden = ((kMacro2 - frame.origin.y) / (frame.size.height - 1));
    CGFloat scrollOffset = scrollView.contentOffset.y;
    CGFloat scrollDiff = scrollOffset - self.previousScrollViewYOffset;
    CGFloat scrollHeight = scrollView.frame.size.height;
    CGFloat scrollContentSizeHeight = scrollView.contentSize.height + scrollView.contentInset.bottom;

    if (scrollOffset <= -scrollView.contentInset.top) {
        frame.origin.y = kMacro2;
    } else if ((scrollOffset + scrollHeight) >= scrollContentSizeHeight) {
        frame.origin.y = -size;
    } else {
        frame.origin.y = MIN(kMacro2, MAX(-size, frame.origin.y - scrollDiff));
    }

    [self.navigationController.navigationBar setFrame:frame];
    [self updateBarButtonItems:(1 - framePercentageHidden)];
    self.previousScrollViewYOffset = scrollOffset;
}

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    [self stoppedScrolling];
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView
                  willDecelerate:(BOOL)decelerate
{
    if (!decelerate) {
        [self stoppedScrolling];
    }
}

- (void)stoppedScrolling
{
    CGRect frame = self.navigationController.navigationBar.frame;
    if (frame.origin.y < kMacro2) {
        [self animateNavBarTo:-(frame.size.height - kMacro1)];
    }
}

- (void)animateNavBarTo:(CGFloat)y
{
    [UIView animateWithDuration:0.2 animations:^{
        CGRect frame = self.navigationController.navigationBar.frame;
        CGFloat alpha = (frame.origin.y >= y ? 0 : 1);
        frame.origin.y = y;
        [self.navigationController.navigationBar setFrame:frame];
        [self updateBarButtonItems:alpha];
    }];
}