I2c , the master read single byte , the flag UCRXIFG is not reset as it should be. Why?

Uint16 I2CWaitToStart (void)
{
	Uint32 I2CWatchCounter = I2C_BUSY_CYCLES;
	   I2CWatchCounter = I2C_BUSY_CYCLES;
		while (((UCB1CTL1 & UCTXSTT))&& (--I2CWatchCounter));// Start condition sent?
		if (I2CWatchCounter==0)// then error
		{
			I2CErrNum = SET;
		//  return FAIL;
		}
		return OK;
}

Uint16 I2CWaitToStop (void)
{
	Uint32 I2CWatchCounter = I2C_BUSY_CYCLES;
	I2CWatchCounter = I2C_BUSY_CYCLES;
	while (((UCB1CTL1 & UCTXSTP))&& (--I2CWatchCounter));
	if (I2CWatchCounter==0)// then error
	{
		I2CErrNum = SET;
	   return FAIL;
	}
	return OK;

}
Uint16 I2cRdMng_4 (Uint16 numRd, unsigned char * Rdbuf)
{
	Uint16 rslt;
	Uint32 I2CWatchCounter = I2C_BUSY_CYCLES;
	Uint16 RdIndx = 0;
	Uint16 NumOfRd = numRd;
	Rdbuf [0] = Rdbuf [1] = 0;// for debug only. forbid in the operation state<<<<<<<.
	if (NumOfRd == 0 )
	{
		return TRUE;
	}

	UCB1CTL1 &= ~UCTR;// config as read.
	I2CWaitToStop ();
	UCB1CTL1 |=  UCTXSTT;// transmit the address with the start condition.
	I2CWaitToStart ();
	//--this section deal with reading single byte only, --------------------
	if (NumOfRd == 1) /* if need to get only one byte
						* the procedure is a little different.
						*/
	{
		UCB1CTL1 |= UCTXSTP;// generate stop condition.
		Rdbuf [0] = UCB1RXBUF;//UCRXIFG is automatically reset when UCxRXBUF is read
		return TRUE;
	}
	//----------------------------------------------------------------------------

	/* after the start condition ( the transmitted with the address)
	 * the master need to wait for the ack from the slave.
	 * ( after that neck, the master receive the data and send ack,
	 * therefore the only ack that the master received is after sending
	 * the address.
	 */
	rslt = I2CCheckNack ();/* if nack then the transaction is end here
						* the address need to be ack.
						*/
	if (rslt == TEST_FAIL)// receive nack, and stop the transaction.
	{
		return FAIL;
	}
	while (NumOfRd)
	{
		NumOfRd--;

		I2CWatchCounter = 2*I2C_BUSY_CYCLES;
 		while ((((UCB1IFG & UCRXIFG)==0))&& (--I2CWatchCounter));
 		if (I2CWatchCounter==0)// then error
 		{
 			I2CErrNum = SET;
 		//  return FAIL;
 		}
 		if (NumOfRd)
 		{
 			Rdbuf [RdIndx] = UCB1RXBUF;//UCRXIFG is automatically reset when UCxRXBUF is read
 			RdIndx++;
 			if(NumOfRd == 1 )// only one byte left.
 			{
 			   UCB1CTL1 |= UCTXSTP;// generate stop condition.
 			   _no_operation();// for debug.
 			}
 		}
 		else //NumOfRd == 0
 		{
 			Rdbuf [RdIndx] = UCB1RXBUF;
 			//I2CWaitToStop ();// check it before the next transaction.
 		}
	}
	__delay_cycles(I2C_STANDARD_DLY_BETWEEN_TRNSC); // for debug,

	_no_operation();
	return OK;
}