CAPT OF A DORNIER 328 OVERSHOT ASSIGNED DSCNT ALT RESULTING IN ATC INTERVENING TO REMIND CREW OF THEIR ALT ASSIGNMENT AS THEY HAD ALREADY OVERSHOT BY ALMOST 1000 FT. THE FO RETURNED THE ACFT TO ASSIGNED AT ONCE.

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CAPT'S LEG. WE WERE CLRED FROM FL230 TO FL190 AND TO EXPECT XING TOMSN (ON THE FQF 306 DEG RADIAL; D55) AT 17000 FT. I ACKNOWLEDGED THEM (THE CTLR) WITH A REPEAT BACK OF INSTRUCTIONS. THE CAPT THEN BEGAN DSCNT TO FL190; WHICH I SET IN THE ALT PRESELECTOR. I THEN BECAME BUSY LOOKING UP A MULTITUDE OF LNDG SPDS (NORMAL; RESIDUAL ICE; CYCLE ICE). WITHOUT NOTIFYING ME; HE SELECTED 17000 FT IN THE ALT PRESELECTOR. I WAS NEVER AWARE OF THIS UNTIL I HEARD THE CTLR SAY 'ACR X FL190; 190' (WE WERE DSNDING THROUGH 18100 FT) AS I WAS JUST FINISHING LOOKING UP THE LNDG SPDS. I THEN ACKNOWLEDGED FL190 AND WE IMMEDIATELY BEGAN A CLB BACK UP TO FL190. I ASKED THE CAPT WHAT HAPPENED AND HE SAID 'THAT WAS ME; I SET THAT ALT IN THERE.' HE NEVER DID EXPLAIN TO ME LATER THE REASON FOR HIS ACTIONS. THIS PARTICULAR CAPT WAS THE TYPE THAT WOULD ACCOMPLISH A LOT OF THE FO'S TASKS WITHOUT NOTIFYING HIM; THEN FORGET HIS OWN! THIS WAS A GOOD EXAMPLE TO ME OF HOW THINGS CAN GET OUT OF HAND WHEN THERE IS A LACK OF GOOD CREW COORD AND RESOURCE MGMNT.