A CPR FLC FLYING A CITATION FAILS TO LEVEL OFF AT THEIR ASSIGNED ALT.

Narrative

ENRTE FROM PWK TO BNA; WE WERE AT CRUISING ALT OF FL330. I NOTED THAT ACCORDING TO OUR FMS; BECAUSE OF THE INCREASED HEADWIND AT FL330; WE WERE GOING TO BURN JUST AS MUCH FUEL AND TAKE LONGER TO GET TO BNA AS IT WOULD AT FL290. THE SIC REQUESTED FL290. THE CTLR CLRED US TO FL310 AND AT THE SAME TIME GAVE US ANOTHER SQUAWK CODE. WHILE THE SIC CHANGED THE XPONDER CODE; I SET FL310 IN THE ALT PRESELECT AND STARTED THE DSCNT. I NOTICED THE ALTIMETER AS WE WERE DSNDING THROUGH APPROX FL308.5. I LOOKED AT THE PRESELECT AND IT WAS SET TO FL290. I ASKED THE SIC 'WERE WE CLRED TO FL290; BECAUSE THE LAST THING I REMEMBER HEARING WAS FL310?' HE SAID HE WASN'T SURE AND THAT WE HAD BETTER STOP THE DSCNT. I IMMEDIATELY COMMANDED THE AUTOPLT TO LEVEL OFF; WHICH OCCURRED AT JUST BELOW FL307. AS THE SIC WAS ABOUT TO VERIFY ASSIGNED ALT; CTR CALLED AND ASKED US TO VERIFY LEVEL AT FL310; AT WHICH POINT I INITIATED A CLB. THE SIC RESPONDED THAT WE WERE AT FL307 CLBING BACK TO FL310. AFTER RESETTING THE XPONDER; THE SIC RESET THE ALT PRESELECT TO FL290 WITHOUT MY KNOWLEDGE. HE SAID HE DIDN'T KNOW I HAD ALREADY RESET THE ALT; AND SINCE HE HAD REQUESTED FL290 THAT IS WHAT HE DIALED IN; EVEN THOUGH HE READ BACK FL310 TO THE CTLR -- A MENTAL LAPSE. TO CORRECT THIS PROB; WE HAVE DECIDED THAT ONLY THE SIC (R SEAT; PNF) SHALL SET THE ALT PRESELECT AND THE PIC (L SEAT; PF) WILL CONFIRM VISUALLY AND VERBALLY.