UIImageView's image does not respect ScaleAspectFit contentMode unless the image originated as a CGImage

ViewController.swift

// Assume these return images from disk purely as CI and CG images
let ciImage = createPureCIImage()
let cgImage = createPureCGImage()

// This fetches the imageView reference
let imageView = getUIImageView()
imageView.contentMode = .ScaleAspectFit

// this will not show aspect fit
imageView.image = UIImage(CIImage: ciImage)

// this WILL show aspect fit
imageView.image = UIImage(CGImage: cgImage)

// this will also show it, assume convertCIImagetoCGImage does just that
imageView.image = UIImage(CGImage: convertCIImagetoCGImage(ciImage))