Pro Mini hangs in sleep after a number of successful wakeups

Development Tools IDE 1.x
1

Hello, World!
I have a cheep chinese Pro Mini with ATmega168PA. I made some changes in order to reduce the power consumption - removed voltage regulator and changed the oscilator cristal 16 MHz to 32 kHz one. I burned LilyPad bootloader, that runs 8 MHz internal RC oscilator. Then I ran this code:

in setup() :

void setupSleep()
{
  /*** Configure timer 2.***/
   TCCR2A = 0x00;  //overflow 0xFF (:256)
   TCCR2B = 0x05;  //5 gives 1 sec. prescale (clk/128)
   TIMSK2 = 0x01;  //enable timer2A overflow interrupt
   ASSR  = 0x20;   //enable asynchronous mode  AS2=1 xtal
  sei();
  set_sleep_mode(SLEEP_MODE_PWR_SAVE);    
}

in loop() :

void enterSleep(uint16_t t, uint16_t mils)
{
  power_adc_disable();
  power_spi_disable();
  power_timer0_disable();
  power_timer1_disable();
  power_twi_disable(); 
 
  seconds=0;
  TCNT2 = 0;  			// null counter
  while(seconds<t){
    sleep_enable();
    sleep_mode();   // Now enter sleep and power down
  
//---- The program will continue from here after the timer timeout ----
    sleep_disable(); // First thing to do is disable sleep.
 //   Serial.println(seconds);
  }
  mils>>=2;
  if(mils!=0){
    /*
    TCNT2 = -mils;  // set counter
    sleep_enable();
    sleep_mode();   // Now enter sleep and power down
    
  //---- The program will continue from here after the timer timeout ----
    sleep_disable(); // First thing to do is disable sleep.
    */
  }    
  power_all_enable(); // Re-enable the peripherals. 
      
}

T2 interrupt :

ISR(TIMER2_OVF_vect)
 {
   ++seconds;
   digitalWrite(A3, !digitalRead(A3));   // heart beat LED
 }

All works fine, but after certain time hangs. Heart beat LED also stops. When I change enterSleep() to delay() there are no hanging. I think that internal 8 MHz RC oscilator can't start again for some reasons?
Is it posible to tweak some registers or fuses for stabilising the RC oscilator?

2

Today I found that direct write to TCNT2 causes the problem.

TCNT2 = 0; // null counter

PDF says:
" 18.5.2 Compare match blocking by TCNT2 write
All CPU write operations to the TCNT2 Register will block any compare match that occurs in the
next timer clock cycle, even when the timer is stopped. This feature allows OCR2x to be initial-ized to the same value as TCNT2 without triggering an interrupt when the Timer/Counter clock is
enabled. "

Should we understand that this applies to normal mode too? And that all interrupt souces are blocked?

Apparently this blocking along with sleep() causes deadlock?

Please, give any suggestions to circumvent the problem. I still don't want to go to CTC mode.