ALTDEV ALT EXCURSION IN A NON ADHERENCE TO ATC CLRNC INSTRUCTION.

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AT FL330 ENRTE TO MSY; CTR GAVE A CLRNC TO BE AT FL280; 105 MI N OF MSY. WE WERE STILL A GOOD DISTANCE FROM WHERE WE NEEDED TO BEGIN THE DSCNT. CLOSER TO MSY BUT BEFORE OUR FMS BEGAN DSCNT POINT; CTR SAID THEY NEEDED US OUT OF FL330 AND TO DSND TO FL310. THE COPLT READ BACK OUT OF FL330 FOR FL310. I THOUGHT THIS DSCNT WAS FOR POSSIBLE TFC AT FL330 AND THAT THE OTHER RESTRICTION STILL APPLIED. UPON REACHING FL310 I CONTINUED THE DSCNT TO FL280. APCHING FL295 CTR ASKED US WHAT ALT WE WERE AT. WHEN WE TOLD THEM; WE WERE TOLD TO CLB IMMEDIATELY BACK TO FL310. ABOUT THIS TIME WE GOT A TA ON THE TCASII FOLLOWED BY AN RA 'MONITOR VERT SPD' WHILE WE WERE IN THE CLB. THE OTHER ACFT; A CPR JET; WAS GIVEN A VECTOR AND/OR ALT CHANGE BY CTR. THE TCASII WORKED AS ADVERTISED. UNFORTUNATELY; MY BRAIN DID NOT. WE SHOULD HAVE CONFIRMED WHETHER OR NOT THE ORIGINAL RESTRICTION HELD WHEN GIVEN THE ALT CHANGE TO FL310. SUPPLEMENTAL INFO FROM ACN 237647: SEVERAL MINS LATER; ATC CALLED AGAIN AND SAID; 'WE NEED YOU OUT OF FL330; DSND AND MAINTAIN FL310 NOW.' BOTH THE PLT AND I FOCUSED IN ON THE 'WE NEED YOU OUT OF FL330' PART OF THE XMISSION AND FIGURED HE HAD A CONFLICT AT FL330 AND WANTED US AT LEAST AT FL310 UNTIL MAKING THE XING RESTRICTION. NEITHER OF US SPECIFICALLY REMEMBER HIM RESTATING THAT THE XING RESTRICTION STILL APPLIED. WE ASSUMED THAT IT DID AND DID NOT QUERY THE CTLR TO DOUBLECHK. PERHAPS WE WERE TOO COMPLACENT. BUT I THINK WHAT HE GAVE US AMOUNTED TO AN AMENDED CLRNC; WHICH MEANS THE XING RESTRICTION WOULD BE CANCELLED. WE DIDN'T THINK SO AT THE TIME; BUT SHOULD HAVE DOUBLECHKED! SO MANY TIMES WE GET A DSND NOW CLRNC TO AN ALT ABOVE THE XING RESTRICTION ALONG WITH A RESTATEMENT OF THE XING RESTRICTION; SO PERHAPS WE WERE CONDITIONED TO HEARING IT AND THOUGHT WE DID; EVEN THOUGH HE NEVER SAID IT!