Converting leads combines First and Last name into one field - How do I stop this?

Converting leads combines First and Last name into one field - How do I stop this?

Hi,

When a customer submits their details on our site we take their first name and last name.  This is then listed as First name and Last name in the Lead.  However when we convert a lead to a potential or contact it's combining the names into one field.

How do I stop this happening?

Cheers,
Mark