UICollectionView behaving strangely on IPhone6 Device and iPhone6 simulator

Question

I am working on UICollectionView.I took pictures from iPhone camera using AVFoundation.And i place them in the collectionView. Its behaving strangely on iPhone simulator and original device.

I tested this on iPhone6 simulator its working as expected but not in simulator. and i am supporting only portrait mode.

Actually i don't have iPhone6 device.below are the screenshots from the client. Please look at the below you will get understand the problem those are

1. Images were showing different sizes.
2. Actually there should 5 images aligned in a row
3. Minimum item interspacing is missing

Below is the image i have taken from simulator

Below is the image i have taken from simulator

I am using a different class for layoutView. it has a UIImageView and code corresponding to that imageView

class BLJobCollectionViewCell: UICollectionViewCell {
    let textLabel: UILabel!
    let imageView: UIImageView!

    override init(frame: CGRect) {
        super.init(frame: frame)

        imageView = UIImageView(frame: self.bounds)
        imageView.contentMode = UIViewContentMode.ScaleAspectFill
        self.contentView.addSubview(imageView)
        imageView.image = UIImage(named: "placeholder.png")
        self.imageView.clipsToBounds = true
    }
.....
}

code for collectionView and flow-layout

var flowLayout = BLCollectionViewStickyheaderFlowLayout()
    //flowLayout.itemSize = CGSizeMake(78, 78)
    flowLayout.scrollDirection = UICollectionViewScrollDirection.Vertical
    flowLayout.sectionInset = UIEdgeInsets(top: 0, left: 0 , bottom: 0, right: 0)
    flowLayout.headerReferenceSize = CGSizeMake(50, 50)
    flowLayout.minimumInteritemSpacing = 2
    flowLayout.minimumLineSpacing = 2
    self.collectionView = UICollectionView(frame: CGRectMake(0, 50, self.view.frame.size.width, self.view.frame.size.height-50), collectionViewLayout: flowLayout)



    self.collectionView.collectionViewLayout = flowLayout
    self.collectionView.setTranslatesAutoresizingMaskIntoConstraints(false)
    self.view.addSubview(self.collectionView)
    self.collectionView.backgroundColor = UIColor.clearColor()
    self.collectionView.delegate = self
    self.collectionView.dataSource = self
    self.collectionView.registerClass(BLJobCollectionViewCell.self, forCellWithReuseIdentifier: "PhotoCell")
    self.collectionView.registerClass(BLJobCollectionViewAddCell.self, forCellWithReuseIdentifier: "AddCell")

    self.collectionView.registerClass(BLJobHeaderCollectionReusableView.self, forSupplementaryViewOfKind: UICollectionElementKindSectionHeader, withReuseIdentifier: "Header")

code for layout size

 func collectionView(collectionView: UICollectionView,
    layout collectionViewLayout: UICollectionViewLayout,
    sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize{

        if( UIDevice.currentDevice().userInterfaceIdiom == UIUserInterfaceIdiom.Phone && UIScreen.mainScreen().bounds.height == 667){
            if (UIDeviceOrientationIsPortrait( UIDevice.currentDevice().orientation)){
                return CGSizeMake(73,73)
            }
        }
        return CGSizeMake(78, 78)
}

And i am using auto-layout for views displaying. And i run the app on iPod touch its working fine as expected.

And what i want to know why its behaving strangely. Am i missed something . please guide me in proper direction.

And any help should be appreciated. Thanks in advance.