iOS8でNSFileManagerのcreateFileAtPath:が失敗する

ViewController.m

#import "ViewController.h"

@implementation ViewController

- (void)viewDidLoad
{
    /*
    on iOS8 NSFileManager, -createFileAtPath: is not work after -changeCurrentDirectoryPath: correctly.
    -contentsAtPath: and -removeItemAtPath: work fine.
    
    iOS8でNSFileManagerの-createFileAtPath:使うとアプリがクラッシュするようになってた。
    -contentsAtPath:と-removeItemAtPath:は大丈夫っぽい。
    */

    [super viewDidLoad];
    
    NSString *name = @"foo.dat";
    NSData *data = [@"foo" dataUsingEncoding:NSUTF8StringEncoding];
    [self saveDatFile:data name:name];
    data = [self loadDatFile:name];
    NSLog(@"%@", [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]);
    [self deleteFile:name];
}
 
- (void)saveDatFile:(NSData *)data name:(NSString *)name
{
    NSString *dirPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    [fileManager changeCurrentDirectoryPath:dirPath];
    
    NSLog(@"%@", fileManager.currentDirectoryPath); // the correct path is logged on iOS8 or earlier.
    
    [fileManager createFileAtPath:name contents:data attributes:nil]; // crashed on iOS8 device only.
    
    NSString *filePath = [dirPath stringByAppendingPathComponent:name];
    [fileManager createFileAtPath:filePath contents:data attributes:nil]; // setting full path is working fine on iOS8 or earlier.
}

- (NSData *)loadDatFile:(NSString *)name
{
    NSString *dirPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    [fileManager changeCurrentDirectoryPath:dirPath];

    return [fileManager contentsAtPath:name]; // works fine.
}

- (void)deleteFile:(NSString *)name
{
    NSString *dirPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    [fileManager changeCurrentDirectoryPath:dirPath];
    
    BOOL flag = [fileManager isDeletableFileAtPath:name];
    if(flag == YES){
        NSError *err;
        [fileManager removeItemAtPath:name error:&err]; // works fine.
    }
}

@end