SuiteScript: CommitLine adds new lines in custom sublist

Hi

I have a custom sublist and I have a fieldchange event and I can successfully modify a line in that custom sublist. But When I try and commit the line, to prevent the user from clicking OK all the time, it does commit the line, but also generates a new line! I cannot work out why. Code below.

                //CHECK IF THE ACTIONED CHECK BOX HAS BEEN TICKED AND IF IT HAS, POPULATE THE ACTIONED BY AND ACTIONED DATE

                if (sublistName === 'recmachcustrecord_inspecrecchecklistitms' && sublistFieldName === 'custrecord_inspecrecchklstitmsactioned'){

                    log.debug('line number is',line)

                    currentRecord.selectLine({sublistId:'recmachcustrecord_inspecrecchecklistitms',line: line})

                    //Check if actioned is ticked