Thats a strange one, indeed.
to fix the problem, I edited the checkQTY() function, and added parseInt() to the if statement that evaluates the available Quantity and the entered quantity:
if(parseInt(qty) > parseInt(availQTY)) {
function checkQTY(qty,availQTY) {
var qtyMessageSpan = document.getElementById('inventoryMessage');
var button = document.getElementById('LEDCart_1_ATCButton');
if(parseInt(qty) > parseInt(availQTY)) {
qtyMessageSpan.innerHTML = '<br><br>Sorry there are only '+availQTY+' available. Please lower the quantity and click anywhere on the page.';
button.style.display = 'none';
} else {
qtyMessageSpan.innerHTML = '';
button.style.display = 'inline';
}
}
