Receiving message to the modem

[infinitemind2]

Having trouble reliably receiving messages.
My data is mainly going out-bound but i check if there is incoming message to act on.
So far i get some messages, this is a problem.

A successful receive debug output...
+SBDIX: 0, 10, 1, 1, 11, 0

OK
SBDIX MO code: 0
SBDIX success!
Incoming message!

AT+SBDRB
Waiting for response AT+SBDRB
<< .AT+SBDRB.[Binary size:11]............[csum:1176]Waiting for response OK

A failed one with a message wait (i thought)
+SBDIX: 0, 11, 1, 2, 11, 0

OK
SBDIX MO code: 0
SBDIX success!
Stopping Modem

Next success...
+SBDIX: 0, 13, 1, 3, 11, 0

OK
SBDIX MO code: 0
SBDIX success!
Incoming message!

AT+SBDRB

These three messages, the failed one was using
int sendReceiveSBDText(const char *message, uint8_t *rxBuffer, size_t &rxBufferSize);
with message set to a string, whereas the other 2 did happen to be message set to NULL.
And just tested it with a text message and it worked.

Any ideas what is wrong

Thanks

[infinitemind2]

have had a play with the source code of the library and separated if (mtCode == 1 && rxBuffer)

if (mtCode == 1) // retrieved 1 message
{
diagprint(F("Incoming message!\r\n"));
if (rxBuffer)
return doSBDRB(rxBuffer, prxBufferSize);
if (prxBufferSize)
*prxBufferSize = 0;
}

It seem to work now??????

Doesn't make sense?