GOV SMT DEPARTED A NON TWR IFR WITHOUT GETTING A RELEASE FROM DEP CTL.

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RECEIVED SECOND IFR CLRNC (EMA DIRECT SMO) FROM PT MUGU CLRNC/DEP CTL WHILE ON GND AT CAMARILLO ARPT. (PREVIOUS CLRNC RECEIVED FROM PT MUGU WHILE OPERATING IN THE SAME AREA FROM THE SAME ARPT. CONFIRMED TO CALL AIRBORNE AFTER RECEIVING IFR CLRNC.) ON THIS DEP; I TOOK OFF THINKING THAT I AGAIN WAS TO CALL AIRBORNE AFTER RECEIVING THE IFR CLRNC. MUCH TO OUR (ME AND CTLR) SURPRISE DEP ATC OF PT MUGU DIDN'T EXPECT ME TO BE AIRBORNE AT THAT TIME. THE DEP FROM CAMARILLO ARPT WAS UNEVENTFUL; MAINTAINED VFR THROUGH 1000' AGL AND DID NOT CAUSE A TFC CONFLICT; AS PER ATC. ONE THING THAT MIGHT PRECLUDE SURPRISES OF THIS NATURE FOR PLT AND CTLR IS TO HAVE ATC PROVIDE AN ADVISORY TO CALL ATC PRIOR TO DEP FROM AN UNCTLED ARPT IN EACH AND EVERY ATC IFR CLRNC TO AVOID ANY CONFUSION AND MISUNDERSTANDING. THERE WAS NO INTENT ON MY PART TO DEPART W/O APPROPRIATE INSTRUCTIONS AND ATC ACKNOWLEDGE THAT THERE SEEMS TO BE A COMMON CONFUSION ON PLT'S AND ATC CTLRS FOR THIS TYPE OF DEP FROM THIS ARPT (CAMARILLO ARPT). THE LCL FSDO'S ACCIDENT PREVENTION SPECIALISTS HAVE BEEN BRIEFED BY ME TO PROVIDE A FUTURE HEADS UP. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: RPTR STATED THAT THE REASON HE CALLED AFTER TKOF AND NOT BEFORE WAS BECAUSE EARLIER IN THE DAY HE HAD DEPARTED THE SAME ARPT AND HIS CLRNC INCLUDED AN INSTRUCTION TO CALL NTD DEP CTL AFTER AIRBORNE. WHEN RPTR TALKED TO THE TRACON SUPVR BY PHONE AFTER THIS INCIDENT; HE WAS TOLD THAT THE CTLR EXPECTED HIM TO CALL ON THE RADIO TO DEP CTL FOR RELEASE FROM THE NON TWR ARPT. THIS OCCURRED DURING A VERY LIGHT TFC PERIOD AND NO CONFLICT OCCURRED. THE PRINCIPAL PROB CAUSED BY RPTR DEP W/O RELEASE WAS THAT HE SURPRISED THE DEP CTLR.