Cause Realm to crash when deleting an observed object during observeValueForKeyPath:

ViewController.m

//
//  ViewController.m
//  RealmKVOCrash
//
//  Created by Timothy Costa on 1/19/16.
//  Copyright © 2016 Timothy Costa. All rights reserved.
//

#import "ViewController.h"
#import "UserProfile.h"

static NSString *UserProfileLanguageContext = @"UserProfileLanguageContext";

@interface ViewController ()
@property (nonatomic, strong) UserProfile *profile;
@property (nonatomic, strong) UILabel *label;
@end

@implementation ViewController

- (void)viewDidLoad {
	[super viewDidLoad];
	RLMRealm *realm = [RLMRealm defaultRealm];
	UserProfile *profile = [[UserProfile alloc] init];
	profile.language = @"en";
	profile.userId = 1234;
	[realm beginWriteTransaction];
	[realm addOrUpdateObject:profile];
	[realm commitWriteTransaction];
	
	[self updateProfile];
	
	self.label = [[UILabel alloc] init];
	self.label.text = @"Bob";
//	[self.label addObserver:self forKeyPath:@"text" options:NSKeyValueObservingOptionNew context:nil];
}

- (IBAction)changeLanguage:(id)sender {
	
	[self.profile.realm beginWriteTransaction];
	self.profile.language = [self.profile.language stringByAppendingString:self.profile.language];
	[self.profile.realm commitWriteTransaction];
	
	self.label.text = self.profile.language;
}

- (void)updateProfile{
	[self.profile removeObserver:self forKeyPath:@"language"];
	NSInteger oldUserId = self.profile.userId;
	RLMRealm *realm = [RLMRealm defaultRealm];
	[realm beginWriteTransaction];
	
	if (self.profile){
		[realm deleteObject:self.profile];
	}
	self.profile = [[UserProfile alloc] initWithValue:@{@"language" : @"en", @"userId" : @(oldUserId+1)}];
	[realm addOrUpdateObject:self.profile];
	
	[realm commitWriteTransaction];
	
	RLMResults *results = [UserProfile allObjects];
	self.profile = results.firstObject;
	[self.profile addObserver:self forKeyPath:@"language" options:NSKeyValueObservingOptionNew context:&UserProfileLanguageContext];
}

- (void)updateLabel{
	[self.label removeObserver:self forKeyPath:@"text"];
	self.label = [[UILabel alloc] init];
	self.label.text = self.profile.language;
	[self.label addObserver:self forKeyPath:@"text" options:NSKeyValueObservingOptionNew context:nil];
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context{
	NSLog(@"Observed: %@", object);
	if (object == self.label){
		[self updateLabel];
	} else if (object == self.profile){
		[self updateProfile];
	}
}

@end