problem with elasticMaximumHeightAtTop when I need a negative progress

[junAlex]

Firstly, thank you for this great work, it helps me a lot.We know that elasticMaximumHeightAtTop determine whether can stretch to larger sizes than it's maximumBarHeight,so that, a negative progress.
As code in - (void)setProgress:(CGFloat)progress;

 - (void)setProgress:(CGFloat)progress
{
    _progress = fmin(progress, 1.0);
   //if isElasticMaximumHeightAtTop is YES, a negative progress will not be changed to 0.0.
    if((self.behaviorDefiner && !self.behaviorDefiner.isElasticMaximumHeightAtTop) || !self.behaviorDefiner)
    {
        _progress = fmax(_progress, 0.0);
    }
}

However,code in layoutSubviews did the opposite thing.

- (void)layoutSubviews
{
    [super layoutSubviews];

    // Update height
    CGRect barFrame = self.frame;
    barFrame.size.height = [self interpolateFromValue:self.maximumBarHeight toValue:self.minimumBarHeight withProgress:self.progress];
    self.frame = barFrame;

   //if  isElasticMaximumHeightAtTop is YES, a negative progress will be changed to 0.0
    if(self.behaviorDefiner && self.behaviorDefiner.isElasticMaximumHeightAtTop)
    {
        self.progress = fmax(self.progress, 0.0);
    }
   ......
}

the result is a negative progress will be changed to 0.0 when layoutSubviews.I delete the below code in layoutSubviews for my goal.

 if(self.behaviorDefiner && self.behaviorDefiner.isElasticMaximumHeightAtTop)
 {
        self.progress = fmax(self.progress, 0.0);
 }