Recently, I added a main draggable marker to the map. However, an unusual issue arises when dragging this marker - a blue outline appears around one of the existing markers on the map. This behavior is puzzling as it seems to be triggered by a click event listener attached to each marker. Removing this code snippet eliminates the blue outline but commenting out inner function calls within the click handler does not resolve the problem.

The blue outline occurs across different browsers such as Safari and Chrome, ruling out browser-specific issues.

                    marker.addListener('click',
                            function() {
                                openCloseNav(true);
                                car_park_details(marker);
                            }); 

To see the blue outline example, click here: Blue Outline Example (Rightmost marker)

Below is most of the JavaScript code:

        var markers = [];
        var geocoder;
        var map;
        var mainMarker;

        function initMap() {
            geocoder = new google.maps.Geocoder();

            var defaultCoord = {
                lat : 51.600960,
                lng : -0.275770
            };

            map = new google.maps.Map(document.getElementById('map'), {
                zoom : 15,
                center : defaultCoord,
                minZoom : 14,
                streetViewControl : false,
                controlSize : 33,
                gestureHandling : 'greedy',
                mapTypeControlOptions : {
                    mapTypeIds : []
                },
                styles : [ {
                    "featureType" : "all",
                    "elementType" : "all",
                    "stylers" : [ {
                        "hue" : "#008eff"
                    } ]
                }, {
                    "featureType" : "road",
                    "elementType" : "all",
                    "stylers" : [ {
                        "saturation" : "0"
                    }, {
                        "lightness" : "0"
                    } ]
                }, {
                    "featureType" : "transit",
                    "elementType" : "all",
                    "stylers" : [ {
                        "visibility" : "off"
                    } ]
                }, {
                    "featureType" : "water",
                    "elementType" : "all",
                    "stylers" : [ {
                        "visibility" : "simplified"
                    }, {
                        "saturation" : "-60"
                    }, {
                        "lightness" : "-20"
                    } ]
                } ]

            });

            mainMarker = new google.maps.Marker({
                    map,
                 position: defaultCoord,
                 draggable: true,
                 icon : {
                        url : 'mainmarker.png',
                        scaledSize : new google.maps.Size(30, 30),
                        origin : new google.maps.Point(0, 0),
                    }  
                
             });
            
            google.maps.event.addListener(map, 'tilesloaded',
                    find_closest_markers);
            google.maps.event.addListener(mainMarker, 'dragend',
                    find_closest_markers);

        }


        function geocodeEncapsulation(i) {

            return (function(results, status) {

                if (status == 'OK') {
                
                    var marker = new MarkerWithLabel({
                        map : map,
                        position : results[0].geometry.location,
                        icon : {
                            url : 'pin.png',
                            scaledSize : new google.maps.Size(40, 30),
                            //origin : new google.maps.Point(0, 0),
                        },
                        clickable: true,

                        labelContent : '£' + i.price.toFixed(2),
                        labelAnchor : new google.maps.Point(30, 35),
                        labelClass : "markerdesign",
                        labelInBackground : false,
                        title : i.name
                    });
                    marker.set("carpark", i);
                    


                    marker.addListener('mouseover',
                            function() {
                                marker.set("labelClass",
                                        "markerdesignhover");
                            });
                    marker.addListener('mouseout',
                            function() {
                                marker.set("labelClass", "markerdesign");
                            }); 
                    marker.addListener('click',
                            function() {
                                openCloseNav(true);
                                car_park_details(marker);
                            }); 
                    markers.push(marker);

                } else {
                    //console.log(status);
                }

            });
        }

Simplified Version On Fiddle, Drag the centre marker Simplified Version