ACR WDB DEPARTED GATE ILLEGAL WITH ENGINE ANTI ICE VALVE INOPERATIVE IN ON POSITION.

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DURING THE PERIOD BEFORE PUSHBACK FROM THE GATE; THE ACFT HAD TO BE DEFUELED BECAUSE OF A FUELING ERROR OF SOME 50000 LBS. ALSO THE #3 GENERATOR CSD'S HAD TO BE CHKED FOR PROPER OIL SERVICING WHICH WAS ALSO OVERLOOKED BY MAINT. JUST AS THESE THINGS WERE BEING TAKEN CARE OF; I NOTICED AN AMBER CAUTION LIGHT ON. IT WAS THE ENG #2 ANTI-ICE VALVE DISAGREE LIGHT. THE SWITCH FOR THE ANTI-ICE SYS WAS OFF; INDICATING THE ANTI-ICE VALVE WAS OPEN. THIS HAS HAPPENED NUMEROUS TIMES TO ME IN FLT AND THE ACFT OPERATING MANUAL ABNORMAL PROC CALLS FOR TURNING THE SWITCH BACK ON SINCE NO TEMP OR PERFORMANCE RESTRICTIONS APPLY. I REVERTED TO THIS PROC ALONG WITH APPLYING THE ANTI-ICE ON TKOF PROC AND PROCEEDED TO TAKE OFF AND FLY TO MY DEST WITH THE ANTI-ICE SWITCH ON W/O INCIDENT. THE VALVE CONDITION WAS ENTERED IN THE ACFT LOGBOOK AS A MECHANICAL DISCREPANCY AS I ALWAYS HAVE WHEN THIS CONDITION EXISTED. IT DID NOT OCCUR TO ME TO REFER TO THE MEL. I PERCEIVED THIS TO BE AN ABNORMAL PROC SITUATION AS LISTED IN THE ANTI-ICE SECTION OF OUR ACFT OPERATING MANUAL AND TURNED THE SWITCH ON JUST LIKE ON A NORMAL TKOF REQUIRING ANTI-ICE. THIS EXTINGUISHED THE CAUTION LIGHT AND I APPLIED ANTI-ICE ON TKOF PROC. I APPARENTLY MISINTERPRETED THE ANOMALY AND SHOULD HAVE CONSULTED THE MEL BEFORE DEPARTING THE GATE. SUPPLEMENTAL INFO FROM ACN 93348: IT IS UNCLEAR AS TO WHETHER THE CREW WAS CORRECT IN HANDLING THE SITUATION AS AN ENRTE PROB (WHICH IS WHAT WE DID) OR INCORRECT IN LEAVING THE GATE WITH AN INOPERATIVE COMPONENT THAT REQUIRES PLACARDING BY MAINT.