ACR MLG CLIMBED 1500' ABOVE CRUISE ALT.

Narrative

10 1/2 HRS INTO THE CREW DUTY DAY. CLBED OUT IN MODERATE TURBULENCE AND SOLID IFR TO 17000'. LEVELED OFF. RIDE AND THEN RECEIVED A FREQ CHANGE TO TORONTO CENTER. WITH THE EXCHANGE CAME AN ALTIMETER CHANGE WITH AN INCREASE OF ABOUT 150'. AS THE PNF I SET MY ALT AFTER ANNOUNCING THE VALUE TO THE CAPT. HE RESET IT TO THE CORRECT VALUE AND NOTED WE THEN WERE AT 17100' OR THEREABOUTS. ON THE MLG AUTOPLT; AFTER HAVING LEVELED OFF AT A SPECIFIED ALT; TO RECAPTURE THE NEW 17000' AFTER CHANGING THE ALTIMETER; IT IS NECESSARY TO CHANGE THE VALUE IN THE WINDOW TO 16000' OR 18000' TO GET A VERT MOVEMENT GOING. EXACTLY WHAT THE CAPT DID NEXT IS NOT CLEAR. I LOOKED UP AND SAW 19000' IN THE ALT WINDOW; THE ALTIMETER AT 18500' AND CLBING. I IMMEDIATELY ASKED; 'WHAT ALT ARE WE CLRD TO?' THINKING WE MUST HAVE RECEIVED A CLRNC WHILE I WAS GETTING THE IDENT. THE CAPT IMMEDIATELY STARTED A DES. JUST AS WE STARTED DOWN TORONTO CENTER CALLED AND ASKED OUR ALT. I PAUSED A MOMENT AND SAID; 'WE'RE GETTING BOUNCED AROUND PRETTY GOOD (WHICH WE WERE) AND WOULD BE BACK TO 17000 SHORTLY.' 3000' VVI ACHIEVED THIS END QUICKLY.