How to fix the required fields issue in joomla virtuemart?

Notice:
this scenario exist when the user does not log in or sign in.
Here's the scenario how bugs exist in virtuemart:
1.You need to shop then select one product you want.
2.Add this product to cart.
3.Then Click check out.
4.Then click automatically the "Send Registration" button.
5.Try to put some text in other required field and click the "Send Registration" button again.

then after here's the picture:

 as you observed just like others do even you filled the other required fields the label still in RED color.

then how to solve this?

1. You have to custom code the core code.
2. Go to yoursite.com/administrator/components/com_virtuemart/classes/
3. Open ps_userfield.php in line 664
4. Or try to find this code

if( !formelement ) { continue; }

5. Then insert this code after the code above

document.getElementById(required_fields[i]+'$div_id_postfix').className += 'temp';

6. And save it, now your problem is fixed.

try to comments if problem occur