Unity Input detected multiple times in a press

I have a source MonoBehavior script with these methods:

private void Update () {
    if (Input.GetMouseButton(0)) {
        HandleInput();
    }
}

private void HandleInput () {
    Ray inputRay = Camera.main.ScreenPointToRay(Input.mousePosition);
    RaycastHit hit;

    if (Physics.Raycast(inputRay, out hit)) {
        var position = transform.InverseTransformPoint(hit.point);
        Coordinates coords = Coordinates.FromPosition(position);
        HexCell cell = null;        
        if (!cells.TryGetValue(coords, out cell)) {
            var err = string.Format("{0} is an invalid position and coordinates are improperly calculated: {1}", position, coords);
            print(err);

            throw new System.ArgumentException(err);
        }

        print(string.Format("[{0}] cell: [{1}] {2}", DateTime.Now, cell.id, cell.coordinates));
        OnCellTouched(cell);
    }
}

The mesh is transparent and I get the hexagon (cell) as expected. In the editor, I get a single message output when I click on a cell:

[05.31.2017.14.15.14.2836] cell: [0] [x=0;y=0;z=0]  
[05.31.2017.14.15.15.7359] cell: [197] [x=12;y=-22;z=10]

However, when I build and run the application: single-click on any cell, the following is logged 4 - 6 times per click:

[05.31.2017.14.57.50.1588] cell: [0] [x=0;y=0;z=0]
[05.31.2017.14.57.50.1695] cell: [0] [x=0;y=0;z=0]
[05.31.2017.14.57.50.1861] cell: [0] [x=0;y=0;z=0]
[05.31.2017.14.57.50.2028] cell: [0] [x=0;y=0;z=0]
[05.31.2017.14.57.50.2195] cell: [0] [x=0;y=0;z=0]
[05.31.2017.14.57.52.6195] cell: [197] [x=12;y=-22;z=10]
[05.31.2017.14.57.52.6360] cell: [197] [x=12;y=-22;z=10]
[05.31.2017.14.57.52.6530] cell: [197] [x=12;y=-22;z=10]
[05.31.2017.14.57.52.6691] cell: [197] [x=12;y=-22;z=10]
[05.31.2017.14.57.52.6857] cell: [197] [x=12;y=-22;z=10]

Is it possible that a single click is propagated multiple times by the Unity engine that the editor is ignoring? Since each log entry has a different time stamp (milliseconds), the range difference being 157-170ms.

Is there a "best practice" in the Unity paradigm? Should the handler be async? Should the handler ignore subsequent calls within a certain window?

It seems like this would cause problems when I want to use a single click as a toggle on a hexagon tile.