if condition does not work

I'm trying to connect two Arduinos according to the example in Example

I added a bit of debug prints so the code looks like:

#include <Wire.h>

// Include the required Wire library for I2C<br>#include <Wire.h>
int LED = 13;
int x = 0;
void setup() {
  // Define the LED pin as Output
  pinMode (LED, OUTPUT);
  // Start the I2C Bus as Slave on address 9
  Wire.begin(9); 
  // Attach a function to trigger when something is received.
  Wire.onReceive(receiveEvent);
  Serial.begin(9600);
}
void receiveEvent(int bytes) {
  x = Wire.read();    // read one character from the I2C
  Serial.println(x);
}

void loop() {
  //If value received is 0 blink LED for 200 ms
  Serial.print("x = '");
  Serial.print(x);
  Serial.println("'");
  if (x == '0') {
    Serial.println("Do 0");
    digitalWrite(LED, HIGH);
    delay(200);
    digitalWrite(LED, LOW);
    delay(200);
  }
  //If value received is 3 blink LED for 400 ms
  if (x == '3') {
    Serial.println("Do 3");
    digitalWrite(LED, HIGH);
    delay(400);
    digitalWrite(LED, LOW);
    delay(400);
  }
}

The strange thing is, the terminal gives the following information:

...
x = '2'
x = '2'
x = '2'
x = '2'
x = '2'
x3= '3'
x = '3'
x = '3'
x = '3'
x = '3'
...

However, I never see the expected "Do 3" lines. Why is that? I assume if (x == '3) would return true when x = '3'?

Also I see the x3 = '3'instead of x = '3'... now I print x also while an event is received, but are those in two different threads since the expected text would be "3x = '3'") or "x = '3'3"