UICollectionView self sizing cells. Insert/reloadData breaks layout - swift

Question

Writing this question as my last resort, being stuck on this for few days now. I am trying to implement self sizing cells for UICollectionView with FlowLayout. Everything seem to work fine until I reladData() or do insertItemsAtIndexPaths() while being at the bottom of the collectionView.
This is my Cell:
class FooFoo: UICollectionViewCell {
var label: UILabel!
var text: String! {
didSet {
label.text = text
}
}
override init(frame: CGRect) {
super.init(frame: frame)
setupView()
setupConstraints()
}
required init(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func setupView() {
self.contentView.backgroundColor = UIColor.yellowColor()
label = ({
let view = UILabel()
view.setTranslatesAutoresizingMaskIntoConstraints(false)
self.contentView.addSubview(view)
return view
})()
}
func setupConstraints() {
self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-100-[childView]-100-|", options: nil, metrics: nil, views: ["childView": label]))
self.contentView.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-100-[childView]-100-|", options: nil, metrics: nil, views: ["childView": label]))
}
}
This is CollectionView definition:
collectionView = ({
let layout = UICollectionViewFlowLayout()
layout.minimumLineSpacing = 1
layout.estimatedItemSize = CGSize(width: 300, height: 300)
let view = UICollectionView(frame: self.view.frame, collectionViewLayout: layout)
view.dataSource = self
view.delegate = self
view.registerClass(FooFoo.self, forCellWithReuseIdentifier: "Cell")
view.backgroundColor = UIColor.clearColor()
self.view.addSubview(view)
return view
})()
This is dataSource:
func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return items.count
}
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCellWithReuseIdentifier("Cell", forIndexPath: indexPath) as! FooFoo
cell.text = "FooBar: \(indexPath.item)"
return cell
}
After I fetch additional items, i tried both inserting new array of indexes, or reloading data and the result is the same - broken layout.
I also tried replacing estimatedItemSize with itemSize and it did work just fine, so I am pretty certain its because self-sizing cells.
This is the result: