SimpleButton doesn't call configureButtonStyles when used in InterfaceBuilder

[gunterhager]

The button doesn't appear as expected when subclassed and used with @IBInspectable variables to set up the values for configureButtonStyles like here:

import UIKit
import SimpleButton

@IBDesignable

class DesignableButton: SimpleButton {

        /// Background color for normal state.
    @IBInspectable var backgroundColorNormal: UIColor?
    @IBInspectable var backgroundColorHighlight: UIColor?
    @IBInspectable var titleColorNormal: UIColor?
    @IBInspectable var titleColorHighlighted: UIColor?

    @IBInspectable var shadow: Bool = false
    @IBInspectable var shadowColor: UIColor?
    @IBInspectable var shadowOffset: CGSize = CGSizeZero
    @IBInspectable var shadowRadius: CGFloat = 0
    @IBInspectable var shadowOpacity: Float = 0

    override func configureButtonStyles() {
        super.configureButtonStyles()

        if let backgroundColorNormal = backgroundColorNormal {
            setBackgroundColor(backgroundColorNormal, forState: .Normal)
        }
        if let backgroundColorHighlight = backgroundColorHighlight {
            setBackgroundColor(backgroundColorHighlight, forState: .Highlighted)
        }
        if let titleColorNormal = titleColorNormal {
            setTitleColor(titleColorNormal, forState: .Normal)
        }
        if let titleColorHighlighted = titleColorHighlighted {
            setTitleColor(titleColorHighlighted, forState: .Highlighted)
        }

        if shadow {
            if let shadowColor = shadowColor {
                setShadowColor(shadowColor)
            }
            setShadowOffset(shadowOffset)
            setShadowRadius(shadowRadius)
            setShadowOpacity(shadowOpacity)
        }
    }


}