I have a simple script that rewrites part of a page. Nothing fancy. It just removes a select box and adds an input field and two buttons. One that increases the values of the input field and the other decreases it.

In Internet Explorer (naturally it works in Firefox) when clicking on the buttons (they are images) the form is submitted. This is despite specifying 'return false' in the onclick event.

Is there a bug or shortcoming in IE that I am not aware of?

Code:
function increase(obj)
{
    obj = document.getElementById(obj);
    return obj.value = parseInt(obj.value) + 1;
}

function decrease(obj)
{
    obj = document.getElementById(obj);
    if (parseInt(obj.value) == 1) return;
    else return obj.value = parseInt(obj.value) - 1;
}

function improveSelect()
{
    if (!document.getElementById) return false;
    
    var plateform = document.getElementById('selectholder');
    var quantity  = document.getElementById('quantity');

    // Delete the select field from the document
    plateform.removeChild(quantity);

    // Create the field to hold the quantity
    var input = document.createElement('input');
    input.setAttribute('readonly', 'readonly');
    input.setAttribute('type', 'text');
    input.setAttribute('id', 'quantity');
    input.setAttribute('name', 'quantity');
    input.setAttribute('value', '1');
    plateform.appendChild(input);

    // Create the button that will increment the value
    var increase = document.createElement('input');
    increase.setAttribute('type', 'image');
    increase.setAttribute('id', 'increase');
    increase.setAttribute('name', 'increase');
    increase.setAttribute('src', '/images/arrow_up.png');
    increase.setAttribute('alt', 'More Plates');
    increase.setAttribute('onclick', 'increase("quantity"); return false;');
    plateform.appendChild(increase);

    // Create the button that will increment the value
    var decrease = document.createElement('input');
    decrease.setAttribute('type', 'image');
    decrease.setAttribute('id', 'increase');
    decrease.setAttribute('name', 'increase');
    decrease.setAttribute('src', '/images/arrow_down.png');
    decrease.setAttribute('alt', 'Less Plates');
    decrease.setAttribute('onclick', 'decrease("quantity"); return false;');
    plateform.appendChild(decrease);
}