Autoresizing issue of UICollectionViewCell contentView's frame in Storyboard prototype cell (Xcode 6, iOS 8 SDK) happens when running on iOS 7 only

contentView is broken. It can be also fixed in awakeFromNib

ObjC:

- (void)awakeFromNib {

    [super awakeFromNib];

    self.contentView.frame = self.bounds;
    self.contentView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;
}

Swift3:

override func awakeFromNib() {
    super.awakeFromNib()

    self.contentView.frame = self.bounds
    self.contentView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
}

I encountered the same problem and asked Apple DTS for help. Their reply was:

In iOS 7, cells’ content views sized themselves via autoresizing masks. In iOS 8, this was changed, cells stopped using the autoresizing masks and started sizing the content view in layoutSubviews. If a nib is encoded in iOS 8 and then decode it on iOS 7, you’ll have a content view without an autoresizing mask and no other means by which to size itself. So if you ever change the frame of the cell, the content view won’t follow.

Apps being deploying back to iOS 7 will have to work around this by sizing the content view itself, adding autoresizing masks, or adding constraints.

I guess this means that it's not a bug in XCode 6, but an incompatibility between the iOS 8 SDK and iOS 7 SDK, which will hit you if you upgrade to Xcode 6, because it will automatically start using the iOS 8 SDK.

As I commented before, the workaround Daniel Plamann described works for me. The ones described by Igor Palaguta and KoCMoHaBTa look simpler though, and appear to make sense giving Apple DTS' answer, so I'll try those later.