Animation applies a y translation transform. Why?

gistfile1.txt

- (void)animatePhotosIn
{
    CAKeyframeAnimation *userPhotoAnim = [CAKeyframeAnimation animationWithKeyPath:@"transform"];
    userPhotoAnim.values = [self photoTransformValuesWithMultiplier:1.0];
    CAKeyframeAnimation *matchPhotoAnim = [CAKeyframeAnimation animationWithKeyPath:@"transform"];
    matchPhotoAnim.values = [self photoTransformValuesWithMultiplier:-1.0];
    
    NSArray *photoAnims = [NSArray arrayWithObjects:userPhotoAnim, matchPhotoAnim, nil];
    for (CAKeyframeAnimation *photoAnim in photoAnims) {
        photoAnim.calculationMode = kCAAnimationCubic;
        photoAnim.duration = 1.0;
    }
    
    [userImageView.layer addAnimation:userPhotoAnim forKey:@"userPhotoAnim"];
    [matchImageView.layer addAnimation:matchPhotoAnim forKey:@"matchPhotoAnim"]; 
}

- (NSArray *)photoTransformValuesWithMultiplier:(CGFloat)multiplier
{
    NSArray *translations = [self photoTranslationValuesWithMultiplier:-multiplier];
    NSArray *rotations = [self photoRotationValuesWithMultiplier:multiplier];
    NSMutableArray *combinedTransforms = [NSMutableArray arrayWithCapacity:[translations count]];
    
    for (NSInteger i = 0; i < [translations count]; i ++) {
        CATransform3D translation = [(NSValue *)[translations objectAtIndex:i] CATransform3DValue];
        CATransform3D rotation = [(NSValue *)[rotations objectAtIndex:i] CATransform3DValue];
        CATransform3D combinedTransform = CATransform3DConcat(translation, rotation);
        [combinedTransforms addObject:[NSValue valueWithCATransform3D:combinedTransform]];
    }
    
    return combinedTransforms;
}

- (NSArray *)photoTranslationValuesWithMultiplier:(CGFloat)multiplier
{
    return [NSArray arrayWithObjects:
            [NSValue valueWithCATransform3D:CATransform3DMakeTranslation(multiplier * 200.0, 0, 0)],
            [NSValue valueWithCATransform3D:CATransform3DMakeTranslation(multiplier * -150.0, 0, 0)],
            [NSValue valueWithCATransform3D:CATransform3DMakeTranslation(multiplier * 0, 0, 0)],
            nil];
}

- (NSArray *)photoRotationValuesWithMultiplier:(CGFloat)multiplier
{
    return [NSArray arrayWithObjects:
            [NSValue valueWithCATransform3D:CATransform3DMakeRotation(M_PI_4 / 2.0 * multiplier, 0, 0, 1)],
            [NSValue valueWithCATransform3D:CATransform3DMakeRotation(M_PI_4 * multiplier, 0, 0, 1)],
            [NSValue valueWithCATransform3D:CATransform3DMakeRotation(0 * multiplier, 0, 0, 1)],
            nil];
}