Electronic – arduino – Watchdog timer not being called in sleep mode

On an ATMega328p, I'm trying to setup a program that counts 1 second intervals via the watchdog timer, even when the chip is in sleep mode. A button interrupt puts the chip into sleep mode. The problem I'm having is that once in sleep mode, it seems that the watchdog vector is never being called. I think I have everything setup like it should be but cannot figure out what's wrong. Any thoughts?

#include <avr/interrupt.h>
#include <avr/power.h>
#include <avr/sleep.h>
#include <avr/wdt.h>
//#include <avr/io.h>

#define SLEEP_ENABLED MCUCR & _BV(SE)

void setup()
{
    pinMode(2, INPUT);
    digitalWrite(2, HIGH); //enable pullup

    Serial.begin(115200);

    MCUSR &= ~(1<<WDRF); //Clear WDT Reset Flag

    /* In order to change WDE or the prescaler, we need to
    * set WDCE (This will allow updates for 4 clock cycles).
    */
    WDTCSR |= (1<<WDCE) | (1<<WDE);

    /* set new watchdog timeout prescaler value */
    WDTCSR = 1<<WDP2 | 1<<WDP1; /* 1.0 seconds */
    //WDTCSR = 1<<WDP3 | 1<<WDP0; /* 8.0 seconds */

    /* Enable the WD interrupt (note no reset). */
    WDTCSR |= _BV(WDIE);

    attachInterrupt (0, initSleep, LOW);
}

volatile uint32_t _count = 0;
volatile uint32_t _sleepCount = 0;
ISR(WDT_vect)
{
    _count++;
    //if(PIND & _BV(PIND2))
    if(SLEEP_ENABLED)// && _count >= _sleepCount + 5)
    {
        wakeSleep();
    }   
}

volatile uint8_t _oldADC = ADCSRA;

void wakeSleep()
{
    attachInterrupt (0, initSleep, LOW);

    ADCSRA = _oldADC;
    //setClock16();

    sleep_disable();
}

inline void _doSleep()
{
    set_sleep_mode(SLEEP_MODE_PWR_DOWN);
    sleep_enable();
    //Do actual sleep
    // turn off brown-out enable in software
    MCUCR = bit (BODS) | bit (BODSE); 
    MCUCR = bit (BODS);
    sleep_cpu();
    /////////////////
}

void initSleep()
{
    _sleepCount = _count;
    detachInterrupt(0);

    //setClock8();

    //disable ADC to save power
    _oldADC = ADCSRA;
    ADCSRA = 0;
    /////////////////////////////

    _doSleep();
}

static uint8_t __clock_prescaler = (CLKPR & (_BV(CLKPS0) | _BV(CLKPS1) | _BV(CLKPS2) | _BV(CLKPS3)));
void setClock(uint8_t prescale) //Only call from within an interrup
{
    // Disable interrupts.
    uint8_t oldSREG = SREG;
    //cli();
    // Enable change.
    CLKPR = _BV(CLKPCE); // write the CLKPCE bit to one and all the other to zero
    // Change clock division.
    CLKPR = prescale; // write the CLKPS0..3 bits while writing the CLKPE bit to zero
    __clock_prescaler = prescale;
    // Recopy interrupt register.
    SREG = oldSREG;
    //sei();
}

void setClock16() { setClock(0x0); }
void setClock8() { setClock(0x1); }


void loop()
{
    static uint32_t lastCount = -1;
    if(!SLEEP_ENABLED)
    {
        if(lastCount != _count)
        {
            Serial.println(_count, DEC);
            lastCount = _count;
            delay(100);
        }
    }
    else
    {
        _doSleep();
    }
}