NSButton color (Vibrant Dark) changes by itself

Question

I have a problem with my buttons:

Buttons A and B look good with any connection (@IBOutlet):

Button B looks bad when is connected:

import Cocoa

class ButtonsC: NSViewController {

    @IBOutlet var b: NSButton!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

}

and if I connect the button A, button B looks nice and A looks bad

import Cocoa

class ButtonsC: NSViewController {

    @IBOutlet var a: NSButton!
    @IBOutlet var b: NSButton!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

}

How can I fix it? or what kind of code in my project may be causing that?