AN A319 MCDU DISPLAYED 'CONFIRM UPDATE AT ZZZ.' ACCIDENTAL ACTIVATION OF THAT SELECTION CAUSED A MAP SHIFT THAT WAS CORRECTED WITH ANOTHER UPDATE.

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DURING CRUISE FLT IN NAV MODE TO MLP AND BTWN MLS AND MSP; AN MCDU MESSAGE APPEARED; 'CONFIRM UPDATE AT MLS.' AS THE CAPT AND I LOOKED PUZZLED AT EACH OTHER; HE WENT TO CLR THE MESSAGE; BUT INSTEAD THE MESSAGE WAS CONFIRMED WHEN HE PRESSED THE MCDU KEY. THERE WAS AN IMMEDIATE MAP SHIFT; SO THE CAPT PULLED FOR HDG MODE TO MAINTAIN PRESENT COURSE. THE MAP THEN SHOWED US ABOUT 15 MI N OF OUR NAV COURSE AND OVERFLYING MLS. WE NOTIFIED ATC OF A POSSIBLE POS ERROR AND RECONFIRMED OUR HDG WAS TAKING US TO MLP. THE CAPT AND I CONSULTED OUR FLT MANUALS; SAW HOW THE MESSAGE SHOULD HAVE BEEN CLRED; AND HOW TO AGAIN UPDATE TO A KNOWN POS. WE TUNED THE LWT VOR; WHICH WAS DIRECTLY AHEAD AND ON OUR COURSE FOR RAW DATA AND REQUESTED FROM ATC DIRECT TO LWT THEN DIRECT MLP. ATC DID NOT QUESTION THE REQUEST. USING RAW DATA; WE OVERFLEW LWT AND UPDATED OUR POS ON THE PROGRESS PAGE TO RESET THE MAP. WE CONTINUED TO MLP AND YVR WITHOUT INCIDENT; CONFIDENT OF OUR UPDATED CORRECT POS; BUT WITH CONTINUOUS RAW DATA XCHKS ALONG THE RTE AND IN THE TERMINAL AREA. WE WERE VFR DURING THE ENTIRE INCIDENT AND CLRED FOR A VISUAL APCH UPON OUR ARR TO YVR. I BELIEVE THIS PARTICULAR MCDU MESSAGE SHOULD BE HIGHLIGHTED TO CREWS DURING TRAINING; AS IT CAN INNOCENTLY RESULT IN A SELF-INDUCED GROSS NAV ERROR.