lineSpacing property inside UILabel doesn't work as expected

I am trying to create a custom UILabel class which will allow me to increase the line spacing on a UILabel. I know you can do this in IB with an attributed text string, however it doesn't work if you are using custom fonts. Here is my class code:

import UIKit

@IBDesignable
class SpacingLabel: UILabel
{

    @IBInspectable var lineSpacing: CGFloat = 10.0

    override func awakeFromNib()
    {
        self.renderText()
    }

    override func prepareForInterfaceBuilder()
    {
        super.prepareForInterfaceBuilder()
        self.renderText()
    }

    func renderText()
    {
        var attrString = NSMutableAttributedString(string:self.text!)

       if font != nil
        {
            NSMutableParagraphStyle.defaultParagraphStyle().mutableCopy()
            var paragraphStyle = NSMutableParagraphStyle.defaultParagraphStyle().mutableCopy() as!     NSMutableParagraphStyle 
            paragraphStyle.textAlignment = self.textAlignment

            paragraphStyle.lineSpacing = self.lineSpacing
            paragraphStyle.paragraphSpacing = self.lineSpacing

            attrString.addAttributes([NSFontAttributeName : self.font!, NSParagraphStyleAttributeName : paragraphStyle], range: NSMakeRange(0, attrString.length))
            self.attributedText = attrString
        }

        self.needsUpdateConstraints()
    }

}

This is how it renders in IB (Storyboard):

And here's how it renders in the simulator:

I've tried adding minimumLineHeight and/or maximumLineHeight properties, but these just seem to mess it up in other ways...

So... It turned out that the property lineSpacing is somehow clashing with a possible private variable/property within UILabel. I renamed my property to leading and now it works perfectly.