adjustsFontSizeToFitWidth的意外行为

我想知道为什么我的UILabel在 numberOfLines 设置为1。我用下面的代码设置了一个游乐场:

import UIKit
import PlaygroundSupport

let labelFrame = CGRect(x: 0, y: 0, width: 100, height: 100)
let label = UILabel(frame: labelFrame)
label.backgroundColor = .lightGray
label.text = "Something that's pretty long"

label.baselineAdjustment = .alignCenters
label.adjustsFontSizeToFitWidth = true

label.numberOfLines = 1
label.minimumScaleFactor = 0.1

let frame = CGRect(x: 0, y: 0, width: 300, height: 300)
let view = UIView(frame: frame)
view.backgroundColor = .white

view.addSubview(label)

PlaygroundPage.current.liveView = view

这就是结果

但是,当我改变 生产线数量

import UIKit
import PlaygroundSupport

let labelFrame = CGRect(x: 0, y: 0, width: 100, height: 100)
let label = UILabel(frame: labelFrame)
label.backgroundColor = .lightGray
label.text = "Something that's pretty long"

label.baselineAdjustment = .alignCenters
label.adjustsFontSizeToFitWidth = true

label.numberOfLines = 2   // <<<<<< this is the only change
label.minimumScaleFactor = 0.1

let frame = CGRect(x: 0, y: 0, width: 300, height: 300)
let view = UIView(frame: frame)
view.backgroundColor = .white

view.addSubview(label)

PlaygroundPage.current.liveView = view

结果如下:

这是怎么回事?这是虫子还是我做错了什么?