Filesystem.close very slow

Hardware Arduino Yún
#1

Since i've switched to IDE 1.63 (before 1.61) Filesystem.close function is very slow (5170ms).

      File dataFile = FileSystem.open("/mnt/sda1/GPS.LOG", FILE_APPEND);
      if (dataFile) {
        Serial.println("Write");
        dataFile.println("trara!!!!");
        Serial.print("close ");
        
        timer1 = millis();
        dataFile.close();
        timer2 = millis();
        time = timer2 - timer1;
        Serial.println(time);
      }

What's the matter?

#2

What is speed at 1.61?

1.6.0, 1.6.2?

#3

At 1.60 it is 5ms. There must be something wrong at 1.63.

#4