String containing certain characters causing UITextView to wrap too soon

Context

I am trying to enter a bunch of random text into a text view and character wrap it so the box is completely full of the symbols. It seems as though the text view is trying to be smart about when it wraps based upon certain characters in the text. I have narrowed down the list of characters that causes the text view wrap incorrectly to the following:

] } ) . > / +

The rest of the characters that could be displayed are:

[ < { ( # @ = * ~

The following code run in a Playground will result in a UITextView that has wrapping before the last character in the line.

import UIKit

func generateRandomText() -> NSAttributedString {
    let characterLimit = 9500
    let segmentSize = 500
    // problem characters
    // ] } ) . > / +
    let characterOptions = ["[","<","{","(","#","@","=","*","~","+","]","}",")",".",">","/"]
    let codeString = NSMutableAttributedString.init(string: "")

    while codeString.string.characters.count < segmentSize {
        let addition = NSAttributedString.init(string: characterOptions[Int(arc4random_uniform(16))], attributes: [NSForegroundColorAttributeName : UIColor.whiteColor()])
        codeString.appendAttributedString(addition)
    }

    while codeString.string.characters.count < characterLimit {
        codeString.appendAttributedString(codeString)
    }

    return codeString
}

let textView = UITextView.init(frame: CGRectMake(0, 0, 700, 700))
textView.textContainer.lineBreakMode = .ByCharWrapping

let codeFont = UIFont.init(name: "Menlo", size: 12)
textView.font = codeFont
textView.backgroundColor = UIColor.blackColor()
textView.attributedText = generateRandomText()

Result:

However, the same code without the problem characters produces the results I am looking for.

import UIKit    

func generateRandomText() -> NSAttributedString {
    let characterLimit = 9500
    let segmentSize = 500
    // problem characters
    // ] } ) . > / +
    let characterOptions = ["[","<","{","(","#","@","=","*","~"]
    let codeString = NSMutableAttributedString.init(string: "")

    while codeString.string.characters.count < segmentSize {
        let addition = NSAttributedString.init(string: characterOptions[Int(arc4random_uniform(9))], attributes: [NSForegroundColorAttributeName : UIColor.whiteColor()])
        codeString.appendAttributedString(addition)
    }

    while codeString.string.characters.count < characterLimit {
        codeString.appendAttributedString(codeString)
    }

    return codeString
}

let textView = UITextView.init(frame: CGRectMake(0, 0, 700, 700))
textView.textContainer.lineBreakMode = .ByCharWrapping

let codeFont = UIFont.init(name: "Menlo", size: 12)
textView.font = codeFont
textView.backgroundColor = UIColor.blackColor()
textView.attributedText = generateRandomText()

Result:

Question

What would cause the text view to wrap when a string contains certain characters?