Wake up from deep sleep zeroes RTC memory and will NOT report GPIO as a wake up

[bricomp]

RTC variables are reset to zero when waking up from deep sleep, also esp_sleep_get_wakeup_cause() always returns zero.
The Teensy (3.1 or LC) is providing the reset signal.

Sketch

#define LED 8  // or use LED_BUILTIN for on-board LED
#define INTERRUPT_PIN 4
RTC_DATA_ATTR int bootCount; // = 0;

void setup() {
    Serial.begin(115200);
    delay(1000);

    pinMode(LED, OUTPUT);
    digitalWrite(LED, LOW);

    ++bootCount;
    Serial.println("Boot number: " + String(bootCount));

    print_wakeup_reason();

    Serial.println("Going to blink the LED 10 times");
    blink(10);
    Serial.println("Going to sleep now");
    Serial.flush();  delay(50);
    esp_deep_sleep_enable_gpio_wakeup(1 << INTERRUPT_PIN,
        ESP_GPIO_WAKEUP_GPIO_LOW);
    esp_deep_sleep_start();

    Serial.println("This will never be printed");
}

void loop() { }

void blink(int times) {
    for (int i = 0; i < times; i++) {
        digitalWrite(LED, HIGH);
        delay(1000);

        digitalWrite(LED, LOW);
        delay(1000);
        Serial.print("Blink ");
        Serial.println(i + 1);
    }
}

void print_wakeup_reason() {
    esp_sleep_wakeup_cause_t wakeup_reason;

    wakeup_reason = esp_sleep_get_wakeup_cause();

    switch (wakeup_reason) {
    case ESP_SLEEP_WAKEUP_EXT0:
        Serial.println("Wakeup caused by external signal using RTC_IO");
        break;
    case ESP_SLEEP_WAKEUP_EXT1:
        Serial.println("Wakeup caused by external signal using RTC_CNTL");
        break;
    case ESP_SLEEP_WAKEUP_TIMER:
        Serial.println("Wakeup caused by timer");
        break;
    case ESP_SLEEP_WAKEUP_TOUCHPAD:
        Serial.println("Wakeup caused by touchpad");
        break;
    case ESP_SLEEP_WAKEUP_ULP:
        Serial.println("Wakeup caused by ULP program");
        break;
    default:
        Serial.printf("Wakeup was not caused by deep sleep: %d\n", wakeup_reason);
        break;
    }
}

Debug Message

Port open
Boot number: 1
Wakeup was not caused by deep sleep: 0
Going to blink the LED 10 times
Blink 1
Blink 2
Blink 3
Blink 4
Blink 5
Blink 6
Blink 7
Blink 8
Blink 9
Blink 10
Going to sleep now
Port open
Boot number: 1
Wakeup was not caused by deep sleep: 0
Going to blink the LED 10 times
Blink 1
Blink 2
Blink 3
Blink 4
Blink 5
Blink 6
Blink 7
Blink 8
Blink 9
Blink 10
Going to sleep now