Prova detta;
var onFormItem=false;
window.onblur=function(){if(!onFormItem){window.focus()}}
och:
<form>
<select name="foo" onmouseover="onFormItem=true;" onmouseout="onFormItem=false;" onchange="onFormItem=false; document.body.focus();">
<option>A</option>
<option>B</option>
</select>
</form>