I believe there is a bug in serializeArray whereby using...

<select multiple="multiple" name="test[]">
    <option value="one" selected="selected">One</option>
    <option value="two">Two</option>
    <option value="three" selected="selected">Three</option>
</select>

$('select').serialize();

returns 'test[]=0&test[]=1' instead of 'test[]=one&test[]=three';

I think the problem is line 2094(ish)...

jQuery.map( val, function(i, val){

which should be...

jQuery.map( val, function(val, i){