Unable to receive "+CSDI" URC with MC8775

Hi, I’m doing some test with Sierra Wireless modem 1.8 mc8775 with default configuration.
The only thing I changed is AT+CNMI=2,1,0,2,0. When I send an SMS (pdu mode obviously) with SRR enabled (status report) I never see the +CSDI URC coming back!

I did exactly the same test (same PDU, same configuration) with other 2 gsm modems of different manufacturers and I correctly see the +CSDI URC coming back.

Am I missing some proprietary configuration? Is this a bug?


EDIT: I just discovered that if I set AT+CNMI=1,1,0,1,0 after sending the sms, instead of receiving the +CSD/+CSDI I always get +CMS ERROR: 321 (that is “Invalid memory index”).
Maybe the SMS-STATUS-REPORT is coming back from the network but the device is unable to save it.