write() to serial port (Bluetooth) does not always work except when debugging

[da_cobra]

It's sunday again so time to work on my robot project again...

I have a problem that I can't seem to figure out :

I have a serial communication through Bluetooth between my Raspberry Pi and my PC with Putty.
I use the following code to send text from my RPi to Putty :

int serial::writeSerialPort(char const *string)
{
   /*
   write a string to the serial connection
   */
   int result = write(fd, string, strlen(string)) ;
   tcflush(fd, TCOFLUSH);
   return result ;
}

The strange thing now is that sometimes the text is being send to Putty and that works a while.
Then suddenly it stops working, after a while it starts working again (all in the same session).

When I set a breakpoint and debug my code the text is always being outputted right after the write() function (before the tcflush() ).

This of course makes it hard to find out why I have this "bug".

Anyone that can point me in the right direction?

edit :

I changed my code to

ssize_t serial::writeSerialPort(char const *string)
{
	/*
	 write a string to the serial connection
	 */
	
	ssize_t result = write(fd, string, strlen(string)) ;
	
	tcflush(fd, TCOFLUSH);
	if (result != strlen(string))
		printf("Failed to write to serial port!\n") ;
	else
		printf("Wrote to serial port!\n") ;
	
	return result ;
}

and it seems that the write function always return a value that is equal to strlen(string) so I'm sure that the write() worked!